FNB lawyers harrassing me

FNB handed me over for missing a payment on my cheque account to Hammond and Pole, I did miss the payment and was due to retrenchment and being unemployed for 11 months. I made arrangements with Hammond and Pole and have been paying them on time for the last 14 months. I have paid back almost R80 000 and doing my best to keep it up. I pay Hammond and Pole by the 22nd of most months, but never after the 28th. For the last 4 months I get threatening emails and calls for not paying my account, and every time I have paid my account on time and everytime I send proof of payments, I had to change reference numbers, then emails but it never stops, I spoke to their call centre manager but it just carries on. It really stressed me out because I have done everything they asked me to do and more yet it is just not stopping. If my actions can't speak to these companies about my commitment to do the right thing without being harrassed every month then I don't know.