Most likely explanation is you have a current membership that has not expired yet so the newly purchased membership has stacked to kick in when the current membership eventually expires when it has run its full monthly course.
If you have used up allowances on your current membership and need more to use specific services then you need to buy add-ons - not a new membership.
Your online account will clarify the situation with regard to current membership and expiry date and any "next" membership and start date.
Post back with details if possible.
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.