How do I re-register as an auto-entrepreneur when I already have a SIRET?

I have been registered as an auto-entrepreneur for about four years. It came to my attention mid last year that there was a problem with my registration. Having tried several avenues to try and get to the bottom of it, I was informed that it was on the official record that I had ceased trading on January 21st of this year. I contacted the URSSAF who I finally received a response from in September. They told me that I was de-registered because of a letter that I sent them in January 2011 telling them that I was suspending activities to take up a work opportunity abroad for a period of time.

I returned after 6 months and continued to pay my tax and advise them of change of address until recently. By May I was no longer able to make declarations on the auto-entrepreneur web site. They told me that I could re-register in January next. I am based in France and have a business address but no residential address as I have been abroad on contract. I have asked them to clarify the procedure for re-registration, however they stated that my inquiry required further consideration at a higher level and I have had no reply.

How do I re-register when I have already have a SIRET?