Amazon — Prime membership

Address:	63775
Website:	Amazon

When checking my citi card statement i found charge for $99 for a prime membership. I do not recall authorizing this purchase. I have checked my amazon account and it said i do not have a prime membership. What do i do now? I have already paid my citi card and was checking my receipts against it when i found this charge. I did purchase several items thru amazon for christmas but thru my daughter's account. This charge was dated 12/13/2016. I found it too late to complain to citi card so thought i would try to use it. That was yesterday may 12th. When i opened my account it said i did not have a prime membership. $99 is too much money to let go and i don't understand how my account number for citi bank card was used without my knowledge for this transaction.