If you moved address and changed provider from BT to TT in one go, and that house move was across exchange boundarys ( in other words the old address was off a different exchange to the new address) then TT should not have offered the number port, number ports are about removing barriers to changing providers by removing the need to change the phone number , it's not a process so that you can take a number with you wherever you move to.
If the process had been properly applied when you moved you should have got a new number from TT 3 years ago.
How far apart are the addresses ?, are you sure they are off different exchanges ?
There is a way to get the number at the address, but you would have to port the number you want to a VOIP provider and access it via your broadband , and the 'phone line' would have a new BT number from whatever exchange the address is served from, so you would have 2 numbers , one delivered by VOIP ( the one you want) and a new number that you could use or not use, it would be up to you
