My understanding is that the 12 year rule comes into effect provided that its worded as such in the mortgage deed. There are many who have successfully argued in favour of 6 years.(posted 7427 days ago)I am not sure if one letter in 1999 constitutes sufficient contact. If they sent a letter (recorded delivery or not) and they heard nothing from you, then why did they not chase up the letter with another? Why did they make no attempt to find you?
I suggest that you follow the advice on this site and question the building society on the debt. If the debt was in 1993 then you're coming up to the 12 year end. As far as I know if they haven't started proceedings against you within the 12 years, then that is it. Unless anyone else knows otherwise??