Contact 48 support here and they can give you details of your calls and maybe explain where your minutes went to:
Are you sure that the most recent Don membership is actually active?
Could it be that you have another (e.g. Standard, Guido?) membership active, the Don one has stacked and you ahve used up the 300 mins on the other membership?
What does your online account say about your current membership type and expiry date?
Does your Membership Planner list a next membership and start date?
Hope this helps.