Despicable practices from Rain

I had a Rain 5g router whilst I was living in Johannesburg and never had any problems with it and in fact I was totally happy with the service. I then relocated to Durban and as there was not Rain coverage where I was moving to, I cancelled my Rain subscription. I paid everything that was due. Now, 7 months later, I get a message from a debt collection agency that I have been handed over the last month subscription that was not paid. At no time did anyone from Rain contact me and said that there was an amount outstanding. They had all my contact details, in fact, I still get promotion calls from them. And in fact, the amount was paid, I have now sent proof that it was paid. I was thinking of getting Rain again now that we do have coverage where I live, but this just put the final nail in the coffin. If they do not have the courtesy to give me a call or email, but hand me over to debt collectors for a debt that is not even due, I will never give them any more business. YOU NEED TO DO BETTER.