Bad service

I have a contract with MTN and because of financial issues I didn't pay for about 3 months however I recovered that on the online contract service since the debit order was cancelled but just when my account had been settled and I was about to make a payment for my April premium I could not as it stated my account has been deactivated due to non payment. I contacted the service provider multiple time to no avail, I emailed them and they told me I have an outstanding amount to which they never assisted me in setting up a debit order again I am being harrased by a debt collection agency. So I decided to go online and pay however my account is still deactivated. They are not replying, I have paid but I'm still harrased.