You'll need to provide a bit more information than that if you want assistance from the Community Forum.
What exactly do you mean by "top-up"?
What exactly are you trying to buy?
Monthly membership plan, add-on, cash credit?
What happens when you try?
Any error messages?
When were you last able to successfully buy stuff on 48?
Are you sure that your payment card is still in, not frozen via your online banking, and there are sufficient funds in the account if it's a debit card?
If you need to contact 48 support about this then see the links in my signature below.
