Cellular No Service and Modem Firmware Have error

2 days ago this error get. Repair store in myanmar that I bought it in January 2018, told me they can try to fix this and not sure to good. LoL. 1 year warranty is finished. What should I do with this error? Someone help me please.. cellular is something searching and then no service status is on that left corner. And then sometimes even disappear. Any status is not at that place. 😢 I take out SIM card and put it back but not ok. I reset network setting and update ios 12 with wifi. But not still okay 😢 Apple store said that this can be in one phone of apple among 10 phones. Buying iph is like a lucky dip? Am I unlucky man? 😢 I'm sure I didn't do anything my ph , no wet , no open back , no glass hit both sides, all are fine. 😭😭😭😭😭😭