Your not alone i have gotten poor service myself and left at a huge loss, also on sign up my £100 voucher was NOT honoured and poor resolution t tat but my main issues was with my sim contract from bt..
Not happy with this company, lost my Samsung galaxy 8 with my BT mobile sim contract inside as i used this sim with my handset witch did come from another network but used BT, when i lost my handset my insurance asked for proof of usage witch BT could not give me they had poor excuses to why they couldnt give this info witch i believe they should be as sim was used with that handset in question, i was told till blue in the face they could not provide proof of usage strangely, witch has now caused me big issues with getting my handset replaced by insurance no proof of usage no claim. so now im at a big loss of a £750 handset i cant replace and stuck in a 2 year contract paying £44 a month with no handset, no thanks to BT mobile not providing the appropriate info for my insurance company, when i mentioned court action bt all of a sudden managed to produce documents out of the blue witch did not even gel with my claim, so i believe this is made up and it come across very suspicious i am now forced with having to take court action at a cost to me, as a autism suffer and suffer of Asperger's i found my ordeal very very frustrating and distressing i have been without a handset since Oct now while dealing with this and every day my mental health gets effected and now forced to buy out for a new handset. i believe BT mobile to be liable in this case and having to take them and others to court over this now, id stay well clear of BT for mobile phones they have a poor reaction to customers issues and cant even do the simplest of things and unless you want to lose out i wouldnt even go there. not worth the stresses or action that has to be taken after dealing with them i also managed to gather over £50 worth of phone call charges to my home phone in relations to all contact to companies about issues revolving this. very upset customer and will never use BT again or advise people to go with them. I also had to go through the Ombudsman who sided with my insurance company and denied my claim due to no proof of usage so i feel BT are at fault and liable and act very suspiciously, i had to go through reconsideration with insurance and the ombudsman companies all to a fail due to one simple bit of info BT wont and say cant provide. Soon as a sim is put in to a handset that network is aware and details are logged of this imei number and with that number states what phone is used so why they cant do what other networks do is beyond me.