*********** at collections and incapable of answering phones

This is the second time i have received a demand from Norman Bissett after proving to them via numerous emails and calls that my account with their client, Vodacom, has a zero balance. The account was paid in full and apparently "accidentally" sent to Norman Bissett for collection. I have the proof and documentation from Vodacom but yet N&B insist on harassing me and expecting me to pay for something i have already paid on time and settled 2 years ago when i cancelled the Vodacom contract. Can i see an Attorney to sue N&B for harassment and defamation? I tried calling their offices ALL day today but after holding for long periods of time getting through to an agent only to have the call dropped on numerous occasions i gave up. Keeping up with the level of service we see all over SA today, truly pathetic.