The same has happened with my son's acc, my daughter's acc and our acc. I think it's because of the way Lloyds operate the 'ear-marked funds', basically, when your cards been used the amount is deducted from available balance for a limited time. for some reason Lloyds don't earmark these funds long enough and the available balance goes up again, giving a false impression and allowing you to either use your card or withdraw cash. With my son, as you say, they didn't send a letter until he had racked up £60 and it took days to arrive, ended up him owing around £170!!! He was promised that the charges would be refunded as the bank manager noted that it had not happened before but the charges didn't come off and he was charged the month after which then took him overdrawn again!!!! He eventually got the charges refunded but ended up with a £50 overdraft, the manager said it was just 'incase'. The banks will shun responsibilty by stating that it is the customer's duty to keep a check on their spending and should know how much money they have left to spend...
It's nice to be back......