Large Loan Showing Up, Company Reporting It As Valid When Disputed, But Says They Can't Find Any Information On It When We Call

Location: Texas

So for context, 6 or so years ago we did a voluntary repo. We have the proof of sale showing we sold our mobile home back to the company we bought it from (we were moving into a new home after having a baby and the realtor couldn't sell it himself in time). After that, we were never told we owe anything on the home, and nobody ever got in touch with us saying we needed to make any sort of payments, as far as we knew everything was settled. Well, we are now trying to buy a house, and thought everything was good because our income and credit is where it needs to be to buy.. and now, despite it never showing on our credit when we'd run credit reports, it's showing up as "may be a balance due", and according to the lender, that we have a payment obligation of over $3,000 a month on it. My lender and whoever he works with went through multiple companies trying to figure out more about it, but the company they were told owns the loan has no record of us in our system, and everyone is telling us as far as they see we don't exist as owing anything. We went through equifax to dispute it because of that... and they reported to equifax as it being a valid debt. So we called them again, MULTIPLE times, and are still getting told they have no information of us having any sort of debt with them. We're at a complete loss on where to proceed here. This is the only thing stopping us from buying, and it's not even actually affecting our credit score, just making our debt to income ratio WAY too high. What exactly can we do in this situation?