the timeshare provider forwarded an overdue bill for fees/dues to a credit company and they claim, that for a fee, I can sign a non-use agreement and get out of the contract. I have to issue a letter to the provider myself
You will want to read not only your original contract, but also the non-use agreement carefully to see what you are obligated to do. You should also consider donating the time share property to a charity. There are many charities that accept timeshares, if they are in desirable locations. The benefit is that you get to do a good deed and you also get a tax deduction, as well. I have had a number of clients successfully rid themselves of timeshares in this manner and it has worked well for all concerned.