icloud buying more storage

I was planning to buy more icloud storage, so decided to buy 500gb storage, so I filled everything on the *buy more storage* form, then I clicked DONE. then suddenly after putting my apple id password. a BLANK PAGE appeared on my screen. I thought okay then..so I added the info and clicked DONE,. then the BLANK PAGE came again. so my question is that- why doesn't my icloud storage purchasing work????please tell ,me some solutions.

May 25,2015