Súil, I don't know if it makes any difference but I would have given him a time frame to answer in and then informed him of his default when the time frame was up. When I addressed an agent and used the "you" part I also included their name and capacity behind it so as to not give the option of questioning who "you" is. Not sure if it would change any of the circumstances you are in. Did you also send it registered mail?
Printed copy · Anthology Volume 3, page 936Printed copy from The Tender For Law Anthology, Volume 3, page 936 (printed 13 June 2014). Added by this site; not part of the Facebook export.