Plan changed through internet not performed

Hi,

I had a monthly plan and because I am not using too much the phone, I decided to change it to the Pay as you Go plan, and added fund to my account. I did this change through the website and the change was done (effective 07/01/2013).

This was the theory, because I am reviewing now my account, and is in a curious status, still remains in monthly plan, with funds in the account and with a message "Account refill required".

I tried now again to do the plan change and I am receiving the message that "you need to contact with T-Mobile from your phone". I am now oversees then I can't call.

Someone knows why the change was not done?

Thanks for your help

Sonia