Oyster Card, the great way to get around London's horrible transport mess while using a smartcard automatically topped up with credit. Until, that is, your ‘credit' one day disappears into the abyss and Transport for London is totally unable to explain how or where it has gone.

You can phone their national rate helpline to be told that they only keep journey histories for 8 weeks and can't therefore discern whether your card has been wiped or whether you are lying and actually used the card before that.

The helpline operator (lovely phrase) informed me that she had "never seen anyone's card being wiped before", I suppose implying that I was making up the fact that I'd put £15 of credit on this now pretty useless and empty piece of plastic less than 12 months previously.

Oyster cards do not have an expiry date, at least that is what TFL claims. The credits should stay there forever. Except that in my case, they didn't. The credit disappeared, account reading £0.00.

Two conclusions.

(a) Oyster card has a serious and possibly relatively rare technical problem it isn't owning up to or simply doesn't know about.

(b) My card has somehow been cloned or used fraudulently - Oyster hasn't exactly shown itself to be unhackable in the past, as a Dutch team showed last October. Unikely you'd assume, but it's a possibility.

The disturbing thing is that they don't seem willing to accept that such a thing is possible. This is the sort of closed mind mentality that leads to further problems down the line. If a service convinces itself it is infallible how does it ever find out that it IS fallible?