Harrasment over Paid up Account

My hospital account was settled months ago with the Hospital, yet I’m still being harassed with calls, messages and emails. My Emails and WhatsApps are ignored where i send the proof of payment. This is unacceptable and feels like harassment. I have asked them to stop — the hospital confirmed the account is closed and i am in credit by the way. I have been trying to explain to various callers and none of them not even management understands and has no decency to respond to my mails nor communicate with the Hospital to confirm my payment. They Claim that the calls are recorded and notes are made on the system. YET No one in that entire company is listening to what i am saying and threatening me almost every day. I am forced now to seek my own legal council.