Creditors harrasment

I pay my monthly car instalments via debit order. I received a call from Wesbank collections saying I owe them for November 2016. I then contacted Wesbank and the lady at the call centre said I owe for December 2016. I went and paid high costs to get a bank statement to prove that I paid them. I then received a call from a lady who said I owe for January and then changed and said its for February. Mind you, I was only contacted in September for a 2016 'debt'. They said because I am such a 'good payer' they thought I would pick it up and settle accordingly. I am now harassed by telephone calls of which I get charged interest. Their stories do not add up and I have also since been waiting for the February statement from my bank. The problem now is I am so confused because no one is certain for which 'month' I owe and also because I pay via debit order. I am not sure if I even owe Wesbank or how. If I can get an e-mail from a senior with all statement and payment history from November 2017 until now who explains if I really owe them, how I owe them, how much I owe them, why I only got notified many months later I would be very greatfull. I don't want anyone to call me because mostly they don't know what they are talking about and confuse me further. I have been good with my payments and I have been happy with their service thus far. I wouldn't like our relationship to end in bitter legal battles