Maybe it'll take some time before it upgrades on the self serve?

Can you check the transaction history.

If the screenshot you posted is the current states, you added money on your account.

So there is $30 in your account. Your plan will be expired on 19th.

If you switch your plan to $30 plan now, your 30days start from today. You still have 15 days left on your account, but it will be forfeit.

Best is mark your calendar for 18th and change your plan on 18th manually. (You have enough money in your account to switch to $30 plan) 

And you can set up auto top up. It will renew your account automatically.

Since you’ve already changed your baseplan, the text in the grey box mentions that it could take up to 48 hours for any account changes or payments to be posted. Your payment was processed. All that’s left to do is to wait for the system to catch up and change over to the new baseplan.

The general rule of thumb with prepaid is to wait a day or two before the baseplan renews and then change to a different baseplan. By changing to a different baseplan well before the renewal means you’re not getting the full value of the $35 you’ve spent on your previous baseplan. Mayumi explains this well, pointing out the 15-day forfeiture. 

Thank you guys! I’ll wait until the 19th and then switch over to the new base plan!

I would change your plan on 18th manually before it renewed.