pay as you go credit life?

Hello, just questioning the expiry of Pay As You Go credit.
I"m reasonably sure that I still had 5 pound or what ever at the end of last month, but after this month's auto payment, just checked and it shows 0?
So how long can PAYG credit be stored fir please?

bicboc as long as your SIM stays active then your credit wont expire or time out. Have you checked your usage?

Thanks Martin, that's interesting becasue that account is set to auto renew.
It's unlikely I went over "budget" because I never use my full allowance on this number from the day I've had it.
I use the top up for sending overseas SMS, and was out of UK for most of August?
OK 5 pound is small change, but I was curious - I'd be a bit more agitated if it was 50.
p