VODACOM SA

I had a contract with Vodacom which was to expire in 2 months or so. I requested premature cancellation. Got the quote and made payment, I however made a mistake and duplicated the payment. I payed on the account and someone else had already paid for me using the account number which makes thus doubt payment. Now I request to get a statement and also payed up letter. One the statement will show how much I overpaid then thereafter I request my refund. I made multiple enquiries by sending emails and forwarding proof of payments for this to be resolved. Nothing has been done, the contract cancellation has been processed and the number is back to prepaid which makes it impossible for me to get through their contact center/ billing departments to enquire about this because when I am asked to type the number in question on the call I am told "we do not assist prepaid number" then the call drops. When I call a different department just so I can get to speak to someone, the auto response requests I type the number in question then I get "this number is not in arrears" then the phone drops. It's been over 1 week of not getting assistance, I have sent a couple of emails, no response. I have tried them on their instagram page, no response. Please assist