We had an agreement for a settlement so I can close my debt account

We had an agreement for a settlement so I can close my debt account. All of a sudden when I ask for a paid up letter they’re giving me the runaround. They said I must contact them after 72 hours. When I contacted them again they all of a sudden telling me I can’t get the letter unless I pay the entire amount. I told them it’s not part of the agreement and they stopped responding.