Ok was just a thought, it's a strange one that. I know in the past networks could send you configuration texts to reset your call and message settings in the phone and sim but not sure if that is an option any more. It could be a glitch but I think your phone might not be picking up a setting or getting a bad setting from somewhere. If it were me I would take out the SIM card, clear all the phones cache and reset the phone without the SIM, then put in the SIM to see if the phone picks it up i.e so it does it from scratch, not sure if it would work but hopefully it could help the phone put the relevant settings in the right place maybe clutching at straws