Hi I  supposidely had route canal work on a molar 20 + years ago cant not remember, 1 year ago I had the tooth fitted with new cap over the months the tooth was causing throbbing issues, I thought the tooth was to tight between the other teeth a bulge started to appear in my gum with minor tenderness went back to dentist and he told me route canal was done in the past and I would have to see a endodontic specialstI  waited 12 months for a NHS appointment at Guys and Thomas hospital only to receive a letter saying sorry we can not see you but may be in the future I do not know what to do know the tooth feels dead and I have still a bulge in my gum not causing any reel pain just a dead feeling any suggestion ?
You need to do an IOP AR - X-Ray for the same. As per your past history and pain episodes, you seem to have a periapical cyst.  With this you can either have got your tooth removed or need to Repeat your RCT. Cyst grow slowly but can damage the surrounding tissues. A dead thing is more dangerous than throwing one.