Just to add one small point, you don't "purchase roaming" as such. The ability to roam is a free facility, what you've purchased is a billing add-on to reduce the cost.
This is a popular misconception, and sometimes leads users to travel abroad without enabling roaming - thus finding themselves without coverage abroad.
By means of diagnosis for your issue, do other internet-based functions work on your phone? That would be a good test of whether this issue is connectivity-related or specific to your Google account.
