Mine was. My usage jumped from average 1.2gb per month to over 50, and the buggers billed my £42.40 with no warning (OK they emailed an account I have never used, instead of the one in my contact details)
The first lady I spoke to insisted it was probably my virus checker updating, and the charge would stand !
I was gearing up for a fight, had composed a stinky letter and fired in a Subject Access Request under DPA for all the info re URLs I had supposedly visited, to match it against my work and holiday schedule to prove it wasnae me.
Then the supervisor eventually called back “there were problems with some accounts in December, I have refunded the £42.40 today” which kind if took the wind out of my sails.
So, the PSA aspect – if you think BT have overbilled you – hassle them !