[AC Question]

I sent my Samsung galaxy s4 i9505 away for repairs (USB port changed, screen and digitiser replaced and I asked them to take a look at my antenna, as I get an unusually bad signal) I got my phone today. The charging port was changed and it aprears the have put an aftermarket digitiser on my phone as there is a black bar above the screen. They reported that my antenna was fine but when I got home and turned my phone on I couldn't get a signal at all (I live in a semi rural area but I get 3g coverage) I'm with giffgaff, and this was originally an 02 phone but it worked before. Thanks for any help