Rear camera won't focus after my screen was replaced?

Hi all. I broke my screen and had it replaced - ever since then the rear camera on my phone will no longer focus. I took it back to the repairer and they said that it had nothing to do with them and as the issue was not related to the screen they would not fix it. It seems too much of a coincidence that it stopped working properly as soon as they changed the screen over...

I've taken it to another repairer and they replaced the camera and it STILL doesn't focus properly. I don't really know what to do from here. I've googled it a lot, but I'm not finding anything very helpful. Anyone have an explanation?