Your post was blank @mandyd9023 and the subject line doesn't really provide sufficient information to address your issue.
What happens when you try to buy the €10.99 membership plan?
Any error messages?
Are you using the app or the web interface?
Maybe try switching to the one that you haven't tried in case that makes any difference.
This is the web interface link to try:
What membership plan have you been buying up to now?
Are you sure that you're eligible to buy the €10.99 plan? Not everyone is.
What membership plan options are listed on your Buy Plan page?
If you need to contact 48 support about this then see the links in my signature below.
