No service on iPhone SD (2nd Gen.)

My Phone SE (2nd Generation) will occasionally display "No Service", and will not be able to phone or text. But, when I notice this, if I turn the phone off, wait a few seconds and turn back on, it comes back on, showing several bars, and works fine for a day or two. I don't always notice that it says No Service, so am missing phone calls and texts for some time.

Is there any fix to this? Do I need to replace my phone, it isn't quite 2 years old? Any ideas will be great. Tried contacting my carrier. I did difficulty understanding her, and she couldn't figure out what I was trying to say, she seemed to think it wasn't working right then, not occasionally, so when she had me have someone call me to test it, it was already working. It still doesn't work, very frustrating.