Discovery big error

It has taken discovery over a month to realise they created a problem by paying the service provider a second time after they had told me in the beginning that I had to pay which I did. I sent them the receipts reflecting the payment. And then they have the audacity to try and claim the payment from me. Today Lyndy from discovery apparently phoned the service provider who apparently admitted to a double payment. She then said they (service provider) will contact me as regards the credit. I think discovery knew they had made the error and tried to recoup the money from me instead of admitting they made the mistake. I do not believe they investigated this thoroughly. Only after I escalated it to a dispute with discovery did they all of a sudden realise the problem