You ask whom you should contact to do piles. In my state ( California ) you would call an Engineering Contractor with an A license.
Your state might allow a C27 or equal contractor ( landscaping ) to do this work. To be sure call your county or state building department.

If you live in an area that has a building department that oversees code compliant projects you will be required to have a structural engineer do an inspection and write a report to identify if in fact the wall is structurally sound and can be salvaged. The structural engineering contractor will need this report in order to obtain the permit to start the work.
No inspection= no report = no permit = no work to be performed.

It would be professionally irresponsible for someone to tell you that you could fix the existing structure with steel I beams without seeing and doing a complete investigative site analysis.

In my area ( N. Ca.) not only would a structural engineer be required to write the report but a soils engineer would be required so that the structural engineer could submit the correct mathematical calculations in his report.

so I guess that is one thing to be thankful for. You''re project is not located in the state of California.

good luck.
save those pennies , 30 years is a good run to get out of a wood retaining wall.

If California is at one extreme, parts of Arkansas must be near the other. In my small town there are no permits required or inspection of the construction or repair of retaining walls. Most of my knowledge of walls has come from observing the ones that failed. And there have been many, maybe as many as 200 in a five mile radius over the last 40 years. I've never heard of an injury caused by any of the failures, which makes me wonder if there is any real need for regulating walls under 4 feet in height.

If your neighbor has a wall that threatens you, it's a waste of time to call the city. What works is to call the guy's insurance agent. Faced with the cancellation of their homeowners policy, most will correct the problem.

In our warm climate, wood walls of any type seldom last more than 25 years. But the failure of wood walls under 3 feet tend to be a slow process from first movement to final collapse; often a period of several years.

There are ways to brace wood walls after the deadmen have begun to fail. But it only extends the wall life and often the cost does not justify the repair unless only a few extra years are needed before something else is planned for the site.

So my advice is in agreement with deviant-deziner, "save those pennies".

I wrote a post yesterday, but--duh--must have forgotten to push the final button to commit it. I suggested that you post a picture that is representative of the situation that that we can see what's really up. No guarantees, but at least that gives a fair shot at appraising the situation. If, indeed, as others have suggested, don't put good money after bad (I'm not yet corroborating this yet)...you might be interested in what suggestions follow...where to go from here. I have seen many retaining walls put in where I felt strongly that slope would have been a better--lower cost and lower maintenance--choice.

Anytime I see two less than 4' tall retaining walls very close to each other, I become suspicious that this approach was used to escape meeting retaining wall codes - and not having to use professionals (engineers and soil experts). Typically, a 4' retaining wall (aka, the above ground portion/height) is only part of the height of the wall (the footing is under the ground). Stepping two walls, as you describe, then also requires certain distances from one another - based on soil, wall design, wall height, etc. . . Usually those pushing for taking this approach do so for cost reasons - not for performance reasons . . . and also so that they can do the job (versus what is frequently the better/more secure approach). Of course "customers" like this cheaper approach - at first. While you say your county/State has no code/regulations to retaining walls, I think that only applies to walls that are less than 4' . . . and probably the reason why you have two walls, each at the "proverbial" 4 feet level, combined to retain 8 vertical feet of soil (and more importantly, water saturated soil).

What is being done about water control? Drainage? Is there a drainage system built into the wall design? Is the land above the 1st wall getting watered daily? Water weighs a LOT and is responsible for roughly 90% of retaining wall failures! The other 10% is poor design, miscommunication, post-installation work in the area that puts the wall's retaining ability at risk.

This is what you should do . . . find a very good firm who builds real, full height retaining walls and is licensed. Ask if they have an engineer on staff or how they handle the engineering on their projects. If they can answer that question satisfactorily, then ask them to come out, review, make a recommendation, and provide a quote.