Help 2nd xt720 now gone bad

[Bro]

I am on my 2nd xt720 in 8 weeks.
The back of the first got really hot and the battery died.Then after battery was replaced it would take a very long time to lock on my service provider.After locked,you couldn't make or get a call.
Had it replaced under warranty.
2nd one worked good for 3 weeks.This morning it was off and wouldn't come on.pulled the battery a few times and then it started.
Made a few calls then it stopped working like the first one.
It will show dialing and call ended.
Any ideas what could be wrong?
I am having a really hard time getting it fixed again(8 months of warranty left)

 

[spiderx_mm]

have you tried ur sim card with the other phones? I think your sim card is having some error and the phone is having trouble reading it.

 

[Bro]

I tried my wifes sim in my phone and tried my sim in her xt720.
Its in the phone.Just dont understands how both phones end up doing th same thing.
It sees my provider with full bars.
even wifi will show good strenght but can not connect