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If you had a current membership in place which had not yet expired then any other memberships purchased will have stacked.
Your online account should clarify - in particular the Membership Planner on the right hand side of your My48 home page:
If you buy memberships in advance then you are charged for them up front even if they stack to kick in later.
If you have pre-purhcased a membership or add-on which has not yet started and want a refund then contact 48 support and they may be able to arrange that:
Hope this helps.