Account Overdue

I have an account with Netstar for 5 years now, and i have been paying via debit order, for the past two months i received calls and sms from the creditors, saying my account is in arrears. i have tried calling Netstar several time, and was promised that the matter will be solved and they will call me back. which no one called me back. i don't understand that how come my account is overdue when i'm paying Via debit order. can someone please resolve this or cancel my account with you guys.