Missing Payments and unwillingness to assist with bad attitude from collection staff

I have been with Ackermans for nearing 10 years, i always paid my account on the last day of the month to the Boland Account nr that was provided to me years ago.. I have not been notified of the banking detail change from Ackermans,, and numerous failed attempts to get my statements email to me. Last year Ockter 2017 i wanted to purchase on my account, i was told my account was in arrears, it came as a shock, because i do pay may account every month and more than my amount due per month. i was harrassed by collection with phone calls sms'e,,, After investigiation from myside i sent all proof of payments. They kept harrassing me i spoke with numerous staff Kim Cindy and Fatima to name a few. They managed to allocate 9 of the 11 missing payments. They said that i need to go back to Nedbank to collect the last to payment which in total ar R1800.00 they cannot trace that..I need someone from management to give me a call sort this out and allocate the last to payments, because how can you find 9 and tell me to search for the other 2 myself...??