I believe this is a perspective problem. When money goes into your bank account, it shows as a credit on your bank statement so you think it is a credit in your books... Correct????
WRONG!!!
From the Bank's perspective you put money in, it is a liability. Increasing the balance of a liability account is a credit. But increasing the balance of an Asset account (in Simply these are all the 1000 accounts), is a debit. Money deposited in the bank should be entered as a debit on your books. Money coming out of your bank account is a credit. Mastercard payment back to a customer takes money out of your account so it is a credit. But you have done that entry and that is why your Mastercard receivable is a negative or credit balance.
You need to bring the balance on that account to zero. To bring a negative (credit) balance to zero for a 1000 account, you must debit because you have to increase the balance of the account to bring it to zero.
Your entry above is perfect if you were your bank. But the entry I gave you is the exact opposite because I am posting from your perspective not the bank.
Hope this clears up the mud.