I've been on TER almost forever, and I don't recall them ever having a lifetime membership option. There has always been monthly, quarterly, semi annual, and annual options. They did give lifetime memberships as prizes for certain things such as to the guy who wrote the 1,000,000th review.  

I guess it is possible that they had some limited time offer for lifetime membership that I missed. If you feel like you paid for lifetime membership, and now your membership expired, you need to contact them directly and ask what's up. Use the "contact us" button or email them at [email protected]