Hi, transferred to Three this week, and topped up my account after doing so, but my balance still shows as €0.
Hey @Paul_92720, thanks for posting here. When you top up by the activation amount the credit is used to activate the plan for 28 days from the day you top up. To add additional credit to your balance you would need to top up by less than the activation amount or alternatively if you topped up by more than the activation amount your plan would be activated for 28 days and the remaining credit would be added to your balance.
I'd love to look into this for you and confirm this is the case here. Pop through to me here on PM along with your full name, mobile number, address and date of birth and so I can check the account here for you.