First, I don't want to be alarmist, keep in mind my bad english.
But:
Voice and internet dataplan with Orange Spain.
Still 306 of 600 min., of wich 103 of 300 min. for mobile to mobile calls.
Still 57 of 500 mb (yup!), anyway, when limit reached, conexion slow-down, no overcost.
No sms sent.
No mms sent (LOL).
No change of plan, NOTHING. Period.
The fact: 5.81 € overcost from 23 july until today... detail of this month calls, shows nothing. But the money is there.

Orange issues? Possible, but please, check your bill this month.
We could have some bad-boy-deb in the town.
Regards.

what are you saying? you got a bill for going over your limit on something, but your provider doesn't tell you what it is? the phone can't cause that! i mean sure, it can use minutes or data, but there's no way to hide them from your bill.
if you're not going over any limits, i would suspect some international calls or text messages, or accidental roaming.

I repeat: no roaming, no INTENTIONAL international calls, neither sms sent this month, no premium sms-services (INTENTIONAL).
That INTENTIONAL is the problem my friend.
Until full bill emited by Orange (aprox 23 of this month) I can't solve the issue with them if it is the case.

As I said, NOTHING WITH OVERCOST DONE INTENTIONALLY, this is the reason of the post.

do you got fMMS installed? I was having my credits trickling down, i uninstalled it about the same time my credits had ran out, and now i've recharged no trickling down yet, i don't feel like risking losing money to test if it was fMMS or somthing else though, perhaps fMMS was innocent and the source of the drain was somthing else i dunno

vodafone had me pay about 50 usd a couple of years ago (back when i had my old n95 8gb) forr some alledged extra internet trafic.. even on the bill there were a lot of around 170 mb downloads that i couldnt possibly have made so i confronted them with the phone's log that showed under 500 mb total for that month so eventually after 3 months without phone they admitted their mistake but i had to buy a prepaid sim meanwhile because my subscription was on hold...phew
anyway long story short its possible that they made a billin mistake just dont forget NOT TO ERASE THE LOG oherwise ...
good luck!