A couple of things for you to look into are as follows:
1. If this is a third party collection firm/agency they are likely in violation of the Fair Dept Collection Practices Act. What you should do is next time they call ask them their company name, who the person is that is calling you, where are they located, and if possible get an address. If they don't give an address google the number on your caller ID so you can determine the true identity of the company and if the person on the phone is lying to you. If this is third party and not the company you have a contract with send the company that keeps calling you a letter telling them to stop calling immediately and that you dispute any and all charges to your account. Also, send a copy of the letter to the entity you have the time share agreement with so they are aware of your concerns.
2. Keep a log of every call they make to you with time, date, and contents of the discussion. If you pick up the call make sure to tell them you fully dispute any charges they claim you owe and request they send you a detalied explanation in writing of what they claim you owe and to not call you again but to correspond with you in writing only.
3. If this does not stop within a couple of weeks, I suggest you call a consumer protection attorney and provide your notes and information you have gathered about the harrassement. A good consumer protection attorney you might consider consulting is here: http://www.nunislaw.com/
4. Also, you should contact the attorney general consumer protection division in Texas. The contact information for that specific division is here: https://texasattorneygeneral.gov/cpd/consumer-protection.
What is going on with you is absolutely not okay under any circumstances and I believe can be addressed fairly quickly by following the steps above to protect you from further harrassment, and hopefully get you out of the contract if possible.
With all of the above stated, I am also going to offer you the abiliity to send me privately the contract you have so I can review and give you specific feedback on how you might be able to get out of the agreement altogether if you belive that would be of help to you.
Please feel free to follow up with any questions. I want to help you address this as soon as possible. All the best, David