What do you mean by "credit" here?
What does your My History page say about recent payments/purchases/topups?
What does your My 48 account page say about your current membership status and expiry date?
Does it list any "next" membership(s) in your Membership Planner?
My guess is that you bought two memberships but they stacked rather than starting immediately because your current membership hasn't yet run its full monthly course and expired.
A new membership will only start when the current one eventually expires.
Hope this helps.