Why can't I reconnect to my carrier after screen repair?

I took my Samsung S21 in to have the screen repaired a few months ago and upon receiving it back from the company I used I could not get it to connect to my cell phone carrier anymore. They tried many things to get it to work and after 2 weeks I was basically handed back a paperweight. I'm now reading on here that my original antenna should have been switched into the new screen when they did the repair and I do not believe that this was done. I have also seen that the only way to reconnect to the carrier is to install the original antenna into the new screen unfortunately this is not an option for me as the company I used had actually "disposed" of my screen before they ever even gave me my phone back. I'm trying to see if there is anything possible at all that can be at this point so I'm able to restore service to my phone because the company I used is claiming no fault at all and refusing to Aid me in the repair or replacement of my device essentially telling me not their problem. If you have any sort of solution for me that will save me from having to purchase a new phone (I had only had this one 3 months) I will be greatly appreciative. I know now not to ever recommend this company or go back to them as they have repeatedly ignored any requests from me or the Better Business Bureau about honoring the part of their contract that says any damage done by them would be covered.