I found out a few days ago that I was having the same problem with Playspan, my VPN connection (Virtual Private Network, basically a proxy) was tripping their fraud protection features and cancelling the transaction. I ended up having to use my parent's computer in the US (via a VNC, Virtual Network Computing) to make my payment.

I suggest trying to make your payment from a different location, perhaps a library or net cafe. It's certainly not as secure as doing it from home, but if it's your only way...