TB19,
Welcome to the Community Forums, we appreciate you coming here to get in touch.
I'm really sorry to hear your Dad is having issues with his SIM card. Can I ask if he is a Pay Monthly or pay-as-you-go customer?
I appreciate that he hasn't received any letters regarding his mobile account, but are you able to check with him whether he has received any texts/emails advising that a new SIM needs to be inserted?
Not too long ago, we sent out replacement SIMs as part of some necessary network changes that needed to take place, however we did contact all customers via email/text who would be affected and if they needed a replacement SIM. So this is the reason I ask.
Many thanks,
Beth