Harassment & continued insistence to collect

My Nashua Mobile account was handed over to Mothlanthe Attorneys in Dec2010 and was paid by March 2011. Nashua then approached Nudebt Management, on 01/02/2012 I received demand letter whereupon I forward all the payments made and Nudebt issued me with a paid up letter on 14/02/2012 confirming the account was settled in full.<br> 23 May 2015 Norman Bisset sends me an email demading payment for the same account - 3 years after I received the paid up letter from Nudebt requesting payment but no amount only a reference number - I have contacted Norman Bissett several times telephonically and per email and informed you that this account is paid up there is no outstanding amount due - I have the letters to prove this and yet I continue to receive this demand letters. On the 17/08/2015 I faxed through all my documentation to your offices and have confirmation report. In the last 72 Hours I have received no less than 3 emails demanding payment still no amount stipulated . When i contacted your offices today there is no record of any faxes or correspondence. I Contacted Vodacom as the Vodacom Nashua accounts were transferred to Vodacom and they also confirmed the account is paid up.