The worst BT and Open Reach habit is their random assignment of Engineers to solve problems. When I did have an extended problem with them, some time ago, they must have wasted 10 years of profits from my (modest) account by sending out a stream of Engineers who had not been briefed on the problem and its history, and who stood less chance of solving the issue than my granny.
So if you and Mixture only get called in when there is a customer's issue, and are faced with unbriefed untrained folk, you have my sympathy.