The worst useless company ever

I continually get emailed requesting payment on an account I have no proof of. I have asked numerous times for proof of the debt and I never get a response. I am now receiving emails stating legal action will be taken if I don't pay. How can I pay for a debt I don't know about and with no proof at all. I got 1 mail back stating it has been requested but that is it. Unacceptable and I will not pay a cent of it.