Norman Bisset does not offer any help or assistanc

My Nashua Mobile account was handled by Hammond Pole who have now handed it back to Norman Bisset. originally I was told I owe ZAR 7500.00 - I set up an agreement with Hammond Pole to pay - I paid ZAR 6000.00 towards this. The account was handed over and now Norman Bisset can not find my payment and they tell me I owe ZAR 8500.00 - they can not trace the payments. I have sent all the details and have begged for answers - I send emails clearly stating payments and details on what I was told to pay and they have the audacity to NOT sort out the issue or reply to my mails - they then PHONE me and tell me I owe money - when you try and phone you can never get hold of anyone - when you do they do not acknowledge the mails you have sent that clearly show the amounts advised and the payments made - they keep telling me I owe ZAR 8500.00 - I have been dealing with this since November 2014 and everyone is so useless they can not sort this out and keep telling me I owe money - I should only be paying the balance and feel I should not even have to pay this due to their unhelpfulness and incompetence. No one seems to know what they are doing or can give me an answer. I AM DONE