VPN Express Subscription Renewal Error

Hi,

I have VPN Express (version: 2.3.1) on my iPhone 4S which worked seamlessly until recently. I can use the service but I am low on data/subscription and I cannot buy additional GBs. I get the message "Your Purchase Could Not Be Completed. For assistance, contact iTunes Support at www.apple.com/support/itunes/ww/." (which does not work). (I am not trying to buy additional GBs while in China.)

Anyone know how to solve?

Thanks,

csB