Lifetime membership was a part of a promotional campaign that has already ended on August 25th of 2018. One time payment was all that was needed to get all the bonuses monthly/annual membership(s) provide.
On the membership page, it should read lifetime - paid. If it does not, please contact customer service and we will resolve the issue immediately.
Make sure to register using the same email you've used when purchasing the lifetime membership as well as other details you have provided.