Refund refusal

I have diligently overpaid Vodacom since September 2018 now the account is in credit and I would like a refund of the money as I have closed that account yet I am getting blocked by a requirement for proof of payment (an actual deposit slip – something I do not have as the deposits where an eft and ANY bank only keeps 2 months proof of payment on record!)

I find this very strange that Vodacom has on record the fact that I overpaid my account from September 2018, you have all my private bank statements with proof of payment to Vodacom stipulated yet you requesting documentation that is simply NOT available

Please advise me on the manner in which Vodacom will return my money as I have done all in my power to accommodate an archaic procedure to verify that I have indeed overpaid your organization since September 2018