Accounts not responding

Every few months I receive an Invoice from Vumatel for the line installation. I paid it the first time I had received and sent the proof of payment, yet they continue to send an invoice, every time I reply with my proof of payment and history of previous requests of for payment, but never get any feedback, just another invoice a few months later.

I have tried phoning accounts, they don’t take calls, you can only leave a message asking them to phone you back, and of course they do not phone you back.

Can this please be resolved before you cut me off.