Hello and welcome to JustAnswer. Please note: This is general information for educational purposes only and is not legal advice. No specific course of action is proposed herein, and no attorney-client relationship or privilege is formed by speaking to an expert on this site. By continuing, you confirm that you understand and agree to these terms.
I am sorry to hear about this situation. On this website, I do not always get to give good news, and this is one of these times.
Someone in your situation has little recourse. Allow me to explain why. First, while many verbal contracts are binding, some are not and require a written contract. In Missouri, as well as most other states, a contract for sale of real estate has to be in writing, as well as anything over $500, with few exceptions. See HERE. This is called STATUTE OF FRAUDS.
Therefore, the verbal promise is not binding, arguably.
Second, squatter's rights are not satisfied in such a scenario. Squatter's rights are more properly known as adverse possession, and Missouri requires the following for adverse possession to take effect: actual possession, for 10 years, without permission of owner, open and notorious in doing so, and exclusively by you. See HERE. You had tacit permission to reside there until it was sold (or planned to be sold). So someone in your situation was not a buyer, but a month to month tenant without a written contract - or at least that is how the Court is likely to see it.
Please note: If I tell you simply what you wish to hear, this would be unfair to you. I need to be honest with you and sometimes this means providing information that is not optimal. Negative ratings are reserved for experts who are rude or for erroneous information. Please rate me on the quality of my information; do not punish me for my honesty.
I hope this helps and clarifies. Please use the SEND or REPLY button to keep chatting, or please RATE when finished. You may always ask follow ups at no charge after rating. Kindly rate my answer as one of TOP THREE FACES/STARS and then SUBMIT, as this is how experts get credit for our time. Rating my answer the bottom two faces/stars (or failing to submit the rating) does not give me credit and reflects poorly on me, even if my answer is correct. I work very hard to formulate an informative and honest answer for you; please reciprocate my good faith with a positive rating.