promissory note

What is the name of your state? colorado
i bought a car from my mother and i gave her a promissory note. i stated sending checks but she had difficulty cashing them as they were from out of state and health problems kept her homebound so she requested cash. trust wasn't an issue so i did that and paid most of the promissory note off early. in march, my mother sent me the title of the car and then passed away a little over a month later. now my two sisters acting as my mothers personal representatives demand documentation of payment or the full note will be removed from my portion of the estate. my mother used the cash and didn't deposit it and the only documentation that i have is the car title and a very generic bank statement showing the original checks issued before i started sending cash. the question that i have is will very generic bank statements and the car title be enough to establish that the promissory note was paid?