1999 Toyota Corolla Lower Control Arm Problem

Suspension problem
1999 Toyota Corolla 4 cyl Automatic

Hi- Five months ago, I had to have the front driver's side lower control arm replaced due to an accident. The area made a rattling sound soon after I had this done, but I figured that this was due to the fact that my car is old and the part wasn't original. Five months passed and suddenly the rattling got louder. My brake started to be affected as well. My car still braked fine, but when I would let up from the brake it would catch a bit and then let up. Then, I went over a speed bump and it felt and sounded like the front, driver's side bottom of my car was going to fall out. I immediately took it into a shop and they said that the lower control arm was put in incorrectly. The left side bolt was shimmied in almost diagonally and that the frame had been stripped. Therefore, even when they tightened the bolts, the arm will inevitably come loose over time. They told me to take it back to the place where I had it put on and see if they would make it right, but that I would probably have to go to Toyota since the frame was stripped. I took it back to the shop where the original work was done and they told me that everything was fine--probably because they were the ones that had screwed it up and didn't want to admit fault. They put an extra washer on each bolt just in case. I left the shop and while it's definitely not as loose as it was, it sounds like it did five months prior. Therefore, my question is whether these extra washers will be able to keep the control arm in place? If the hole is in fact stripped (and I don't know why the first shop would lie to me seeing as how they weren't trying to make any money off of me) isn't it still going to inevitably come loose since the bolt doesn't have anything to hold onto inside? Also, the warranty on the original work was for three months, so that has expired.