I have € 2 of calling credit left but I can't call, surf or text. What do I do?

Even though you still have remaining calling credit, this has been reserved by our system for your next data session. This happens because we automatically reserve 20 MB for your next data session.

Your credit should become available again by rebooting your device or by switching to airplane mode. Doesn't this work? Then a new top up will do the trick!