Withdrawal issue with fbs

I deposited with my master card (which was successful), then I executed two order which were all win-win, then I proceed to withdrawal to test how it work, but It quite unfortunate, that I received a email which reads "Your withdrawal request was declined with the following comment:

Your credit card 539983XXXXXX0301 is not valid unless signed. Please sign the back side of the card and repeat a request to VISA/MasterCard / CardPay /Connectum". After receiving this mail, confirmed with my banks, which I got the same results from the two banks, stating that there is no transaction that requires signing the backside of an ATM card.

Please I require clarification on this effect.