When I renew a member's membership the renewal fee is not being charged?

The reason that this is happening is because the renewal fee is determined at the time of sale. If there was no renewal fee defined for the membership at the time of sale, there never will be a renewal fee for that member. When you sell a membership, you are creating a contract. If there was no renewal fee at the time of sale, you can not add one for that member after the sale has been made.