Lifetime Membership is only given if you bought 100 pixels/1 block on
www.signthepage.com which is pretty much spending $100.
If you did buy 100 pixels or one block then pm tault_Admin and wait for a response about why you lost your lifetime membership.
If you didn't buy 100 pixels or one block then you probably just purchased premium membership which costs $14.95 for the first time you use TU's services and then $3.95 for each month afterwards.