Is the Tier upgrade automatic or do I need to request approval?

[_j]

This prior forum thread would seem to apply directly to you also:

Tier 3 Limits - Access didnt become, even paid 100USD

The second sentence above is the correct action needed. The problem will be if you already paid in the maximum tier-1 balance of $100, you will need to make $5+ dollars of usage in order to add any other payment.