My HTC One M8 (unlocked) started perfectly fine for the first two weeks of usage, however for no reason at all the reception just completely went and it it just says limited service on the lock screen, also i tried other sims in the phone but still no reception and limited service although it still detects the sim, i looked up the blacklist to check if my phone imei is on their and checked my phone status and it is compltely fine, when inserting a sim, for example giffgaff, tge phone asks to select the carrier, however when selecting 02 or whatever carrier that sim is, it just says "your sim does not allow a connection to this network", pleeeease heeeeelp, been almost a month now.