iphone 7plus red lossing cellular bars

i bought a new iphone 7 plus and started loosing all the cellular bars at the point that it dint recognize the sim card at all and the cellular menu from settings disappeared. i sent it to the service and it was okay for like 2 month bcs they changed the sim card malfunction . but now it is doing the same thing again. does anyone else had this problem? oh it also overheats a lot during LTE in the sim card area behind iphone