Unprofessionalism from this company

This company always calls me with no facts from their client, they accusing me of owing them money that they cant even prove, even their client cant prove that, but because im not a lawyer, they feel a need of harassing me, they want me to pay the money without question anything. I explained to them several times that i dont owe them or their so called client, otherwise they must come to me with a proof, instead they call me and harassed me everyday without even putting any notes after talking to them