Saftey 1st go and grow issues?

Anyone else have this seat?

I started using these for my twins at 1y.o. they just turned 3, still rear facing and I had to message Saftey 1st because the belt wasn't staying tight. I would tighten it and tug the chest clip a bit to see if I tightened it too much or not enough but it would literally just loosen right back up making it completely dangerous. Not to mention after I stopped using the seat I noticed a metal bar in the back had ripped a hole in the strap itself!

The company sent me a new one, I had to destroy the old one but now the new one is doing AND my other kids seat started doing it😡

Curious how common this is. I hate to message their customer service again and might just bite the bullet and buy a different brand.