problems with iphone 5

To start with, i was 2 years android fan but some time ago i changed my note2/s3 to iphone 5. Operating system ios way better than android in my eyes but iphone quality is way too low for the price of itself. I was using 3 months iphone 5 16gb white with belkin case and didnt see that it has light leakage below power button. 3 days ago went to apple store service in my country they exchanged my iphone to new or refurbished (can't say exactly) within two working days. However i have faced up with signal problem. After 3 hours of using iphone my signal became weak and started to do like this: searching for a while and later no service. Reseting phone did help only for some hours, later "no service" appeared again. Also after night i have lost 15% with idle, no apps running and etc. Today went back to apple service and they took again for replacement my iphone, probably i will get replacement tommorow or monday. I'm a bit ****** that i paid 700 euros and now cant use my iphone and need to drive long way to the service center.

With sim card everything is ok, i was using same sim card with my old one iphone and in 3 months never got "no service".

Both phones was with 6.1.3 software.

By the way anyone also faced up with similar problems, that took a lot of replacements and still suffered some serious issues? :/ because if also new replacement will suffer problems it will be total fiasco.

by the way any technicians here? maybe iphone antenna has some defects or something like that?

thanks for the advices, answers

to add- i have really pleased with apple support, atleast they arent adding more problems...