I paid a higher amount towards my bill. What happens now?

Don’t worry, the additional funds won’t disappear. The money will stay in your account and will be used to pay your next bill. You will then just need to pay the remaining amount.
When you log into either MyGO or the GO app, you’ll be able to see that the balance (highlighted in green) is now in your favour, meaning that you have some extra money that you can use to pay for your next bill.