I had paving stones put in and part of the driveway retaining wall replaced. days after the concrete was put in there was a crack and 4 months later its starting to crumble and issues on the side. the company that did it said it could be from ground moisture. what can I do or should the company fix it. when the wall was put in it rained for several days after.

 

Your wall appears to be somewhat sloppily done. I see lots of smaller, open voids on the vertical face, meaning it was never properly rubbed, and a large void near the bottom. I doubt the visible crack was caused by excessive moisture, but is more likely caused by thermal expansion and contraction, and a lack of any control or expansion joints. How long is the total length of wall? And are there any control or expansion joints in it, anywhere?

Good luck on asking the contractor to make good on repairing the crack. Don't be surprised if he sends a grunt out with a tube of caulk, spending less than 5 minutes to seal it.