Thumbprint is not working, but the home-button its self is working.

I have recently got my IPhone 6 plus screen replaced not that long ago. Whenever I came back to the store they asked me to put my thumb on the thumbprint to unlock it. Note that whenever I broke my broken screen to them my thumbprint was still working and was able to be used. The cracks were near the top of the screen. Whenever I put my thumb onto the phone it was not working. She had asked me if I wanted her to go back into the phone and see if she didn't screw it in all the way. I feel like that is the problem but i cannot find any problems related to mine anywhere. Whenever I go to settings and try to put in a new thumbprint, it goes into the process but the thumbprint preview does not show up. Also, I used to be able to lightly double tap on my home button and the screen would move up but now it won't do it anymore. Is the plate just not screwed in all the way? Do I need to send it to apple for a all in all new home-button? (if that is the case , I will just go ahead and upgrade to the 8-plus.)