Did you send any international texts? They cost 25c each. If you sent three (75c) and your original balance was €10.01 (I think your account starts with 1c balance) then that would explain your balance of €9.26. Note that long texts can actually use more than one SMS under the hood so a single long text could use up 3 SMS messages.
Or could you have used any other services that are charged from your cash credit balance?
http://www.48months.ie/boiler-plate/other-call-charges
With a balance of €9.26 you'll need to top up by at least another €1 to be able to buy €10 membership.
Hope this helps.
