Collection sold and sold and the 7 years keep getting changed

In 11/2006 I request to all 3 credit bureau's that they have a collection removed. The collection agency first reported the debt in Sept 1999 on all three credit reports. All three removed it because it was past 7yrs. I was aware that the collection agency could have sold the collection account since there 7yrs were over to another agency. So I checked my report in March 07 & June 07 to see if they sold the collection and if the new agency were now reporting debt nothing was there. I received collection letter today from the same 1999 collection agency request the debt be paid in full and amount went from $1300 now almost $2600. I looked at my credits report this same agency have added themselves back on my credit report trying to collect same 1999 debt under the same name, same office address & account number. They didn't sell it to anyone else they simply started reporting it again. Are they able to do this. What actions can I take against this company for reporting debt again after 7yrs?
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click here
make them validate the debt
then follow up