Q: No signal

Hello,

I have this problem that's been bothering me for weeks now. My iPhone 6s has "no service" written on the top left part of the screen, meaning no signal, and meaning no calls or messages, or even 3G.

Weeks ago it wasn't this much of a problem, I mean, I had to restart my iPhone and everything would go normally, but it got worse each day. I've contacted my carrier for support but they said that nothing was wrong with my signal, and couldn't understand why I had this problem. Then, I looked up on the internet and tried to find a solution to  problem. I erased all the content from my iPhone and set it as new, but it didn't work. I tried to take ou the SIM card, but it didn't work. Now, I'm completely desparate here. What should I do? I can't use my phone at all when I'm outside because it only works on Wi-fi connection.

please help me. Thank you.