On Monday 29 August at 21:20hrs, I received an email from BT entitled "You're really close to your broadband usage allowance". In it, it reported "You've used more than 22GB of your 25GB allowance this month."
Imagine my surprise to find out I am now being charged £63 for 98Gb of overusage last month (01 Aug 16 - Wed 31 Aug 16).
My grandchildren stayed for 3 days (26th-28th August) and no doubt the reason I went into excess. Trouble is, they had left before I had even recieved a warning email, let alone an exceeded usage email (which I never received). Closing the stable door after the horse has bolted!
I have been using on average about 20Gb a month and am willing to upgrade my account to the unlimited version, but only really happy to do this if the excess charges are dropped.