I spent years working for network operators such as BT, O2, Vodafone, T-Mobile, etc. mostly in operational support systems management. (i.e. the stuff that keeps the lights on.)
These companies are all getting worse, cutting costs and outsourcing work to service companies that don't care much about the quality of what they deliver. The fact that nobody can diagnose a problem as simple as making an outbound call just astounds me. It's almost certainly BT's fault, not Openreach's.
p.s. I still get bills of £0.00 every month from BT, despite leaving them in 2021! Seems like they have completely lost the plot.