Hassle to get my credit amount back from Telkom

I would like to find out why I have to provide proof of payment to Telkom when it already shows on their system that I have a credit amount? I paid viz easy pay at pick n pay in March/April and I think I must have misplaced it but they insist that I go to pick n pay and ask for a reprint but why because the system shows that they owe me money? Hayibo Telkom