Had a similar problem when I applied 4 years back.
Pasting the link to the thread- might be useful for you.
http://www.canadavisa.com/canada-immigration-discussion-board/experts-pls-helpcredit-card-used-to-pay-application-fee-blocked-t43581.0.html;msg307513#msg307513
I sent the payment form along with a covering letter explaining the issue to their physical mailing address. (I included as much details as I thought would help them link this to my file). It worked for me. Relax, it's going to be ok.
Good luck!