I have received a phone call

I have received a phone call from World Financial Network National Bank at my place of employment and he was very rude and told me there was nothing I can do and they he did not have to stop calling or have to prove anything to me…. can any one help I did fax and send a letter today via certified mail with return receipt for validation of the debt and also written notice to have everything be in writing.

Has anyone had to deal with them… please help and give any advice? I am very confused!!!!! I think that simply put – he is breaking the law. There is a Fair Debt Collection law in place to protect you from people like this.