Pathetic service provider - getting unnecessary calls/ harassed everyday

I took a contract with OnAir account number OA- ***5-1. I took a contract with OnAir last year (April 2021) and I’ve been making payments via debit order , what is surprising is that this year I’ve been receiving numerous calls from different people claiming that I haven’t paid my account and I owe an amount of R358.00 , I can confirm these debits are reflecting on my bank statement and when I asked them for which months are they referring to , these people will give me different information with different months. I then requested them to send me statements for these months claiming that are not paid and I was told it will take 14 working days to send me the statement, eventually today they sent the statement and the info on the statement sent doesn’t match with the information I have and my bank statement shows that all my debit orders for OnAir were honored / paid. Please stop harassing me and if I failed to pay in April and May last year why are you only calling me almost a year later. I have the proof that I’ve paid these people