I signed a six month lease in Missouri. I made the monthly payments timely as required by the lease. After 3 months I received a 3 day pay or quit notice from a Results management company,

When I contacted them, I was told that the property was sold shortly after I signed the lease, and that the former owner has not forwarded the payments to Results (the management company for the new owner). I asked why I was not notified to send my lease payments to another party; and the first communication I from them received was a 3 day quit notice 3 months after the fact.

They told me to call the person who leased the house to me and ask him to forward the payments to Results.
When I called the previous owner he said he kept my lease payments because the buyer still owed him money.

Meanwhile I received an email that said Results would honor the lease and to send future payments to them; however they still consider my lease payments to be 3 months delinquent.

What should I do? To whom should I send the lease payments

Send the payments to Results, but only after they prove the property changed hands and they represent the new owner.

Send them a certified letter stating you will make all future payments to them after receiving such proof. Also inform them, that since they were remiss in informing you of the change, then they are responsible for getting the arrears from the previous owner.

If they sue you or try to evict, you go into court with your cancelled checks showing that all rentals were paid and to who, you tell the judge that they never informed you of the change. I won't guarantee it, but I believe the judge will find in your favor.

I am no expert at this but when a person owes somebody money they are not suppose to hold other money back like your landlord is doing to RESULTS.
They should have told you to make your payments directly to RESULTS.
What RESULTS owes them is not your problem.
Make sure you are not getting evicted and make the payments to RESULTS