I don't think it's a good idea to use WMBP at all with Citi and even worse to overpay to a negative balance.

I had done 2 WMBPs to pay off min spend and had a credit balance sitting for months. Finally got around to requesting a credit balance refund.

Within days, got a call from a San Antonio area code 210 number from a Citi rep doing the 'Know your customer' type investigation. Their concern was the anonymous nature of the 2 BPs and source of funds. I explained I had made the payments myself through my own accounts. This seemed to appease them.

Not shutdown but will tread lightly with Citi from now on.