Never been a client but they request payment!

<p>I have received numerous calls and mails from Nudebt who is acting on behalf of their client Nashua Mobile. They have my ID and nothing else and apparently I owe them money, first for a cellphone contract then for a credit card fa****y. There is no contract on file and I have in fact never done any business with Nashua Mobile. How do I get these guys off my back since this is going to negatively affect my credit rating as they have already given me notice to pay within 7 days and warned that the matter will be listed at the credit bureau.</p>