Poor advice received at MTN

I wanted to settle my contract as the installment was high.. I was advised to pay a lump sum, I paid and my acc was still not settled instead they kept debiting from the lump sum I paid. When I asked for a refund of the balance owed to me I was refunded twice and I was unaware of this untill I received an sms saying they will debit R3500 from my account(without my consent/communication).. few months later they blacklisted my name. Just like that.