Three times now (2 in May and once yesterday) they have tried to take the $385 from my current (checking) account and it has failed.

Each time, I have seen a transaction going out to them for the exact balance of my account, down to the penny, leaving me with no money available.

For the ones in May, it took 10 days to resolve and remove the transactions from my account. I can't remember if they disappeared or another transaction credited the money back -- I think they just disappeared.

I've spoken to several support people at my bank about this at length and they've suggested the following explanations:

- coincidence (odds of one in 27 trillion if they were trying random amounts between 0 and £300)

- fraud (doesn't make any sense, I have a good relationship with them and they haven't benefitted anything from these transactions, and I haven't shared my balance with them or seen any suspicious OLB activity)

- a mystery

What's going on here? Assuming my orthodontist's system is requesting $385, how is this translating to a pending (authorised to go out but not accepted yet, I believe) transaction of whatever my current balance is?

None of the support agents I've spoken to has seen this before.

Something to do with currency conversion?