Netstar do not share the value or ethics of paying a refund when its due

I've been a client of Nestar for so many years my account is in credit by 8000.00 , netstar will accept your monthly payment , but don't advise you , you have overpaid month after month , its been 3 weeks I've been trying to get it back, yet you need your DNA to prove its actually you , i understand security measures , this however was not the first incident of the same