If the Don membership has not started yet then contact 48 support and they may be able to refund it so you can buy a Guido instead and when that starts it will cover you while roaming in the EU. It will only start when your current membership expires. If the new Don membership has already started then I don't think that you can do anything but again contact 48 support and ask them if they can do anything for you.
Hope this helps.
I am not a 48 employee so if you need to contact 48 support then use option 3 or the chat facility here.