Your post isn't that clear @Shaunc1191.
You'll need to explain things more clearly if you want assistance from the Community Forum.
What exactly do you mean by "credit"?
Cash credit or a membership plan?
What do you mean by "AddvCredit (add credit?) to phone i bought" and "at (add?) it to my phone"?
What exactly are you trying to do?
If you mean that you have €10 cash credit on your account and you want to use it to buy a €12.99 membership plan then you need to add €3 more cash credit first and then when buying the plan the checkout process should give you the option to pay for us using your €13 cash credit instead of using a bank card.
If you don't have at least as much cash credit on your account as the cost of what you're trying to buy then you don't get that option.
If that's not your issue then please clarify what the actual problem is.
If you need to contact 48 support about this then see the links in my signature below.
