One more thing, I believe the original 15 plan was offering 100 minutes total (in+out) then about month later they cancelled that plan and offered there new 15 plan with unlimited incoming.
Ate you sure you are on the new 15 plan?
If you got the original plan you would have to switch manually from your selfserve.
I believe you can find the details about your plan from the plans and add-on page in the selfserve. If you are still on the old plan switch to the new one, if you need more minutes right away you can do immediately switch, or to save money you can postpone it to your renewal date. You can also purchase 500 minutes for $5 add-on, or if you still have data use fongo or TextNow