You paid off your time share, completing the contract. Make sure you have proof of payoff, statements, cancelled checks, etc. then send them a certified letter saying you are surrendering your week(s) back to the timeshare company so they may use their discretion as to what they do with it. Don’t pay another dime to them or their collection agency. The weeks you didn’t use, were rented to someone else who paid the maintenance fee, you can be sure it didn’t sit there vacant. As you said, you couldn’t even book your own week because they never had vacancies. They double/ triple book these weeks all the time. They are trying to collect the maintenance fee from you even though they’ve collected it from whoever they rented your week to.