Unfair and Non-existing Debt Collection

This company is very abusive and unprofessional, from 2022 they have been abusing me for a debt that does not exist. They claim I was handed over for collection but the said client claims to not have any debt record on me and I am still able to consult with no issues. Their consultants are very rude and have no escalation route, they simple say we will call you until you pay without engaging the issue at hand. I have requested that they put it in writing to me as for which transaction the client handed me over but they are refusing provide such.