I sent a collection agency a letter requesting validation of the debt by certified mail. The Post Office said they have 15 days to sign or refuse to sign. Does this mean they have refused to validate the debt owed and are now in dishonor? Should I now go ahead and do a follow up letter because they failed to validate?

 I sent a collection agency a letter requesting validation of the debt by certified mail. The Post Office said they have 15 days to sign or refuse to sign. Does this mean they have refused to validate the debt owed and are now in dishonor? Should I now go ahead and do a follow up letter because they failed to validate?