Do you really think of a 19mm socket as a special tool? Dumb? David,
clearly you need the correct size socket, first. It should be a 19mm,
but perhaps it has been changed. Sounds like it, for sure, unless your
socket is damaged. Once you have the correct size socket, or wrench,
apply heat to the bolt with your torch. Also,  give the bolt head some
moderate whacks with a hammer. This causes the threads to
release...maybe.
Miguel

Suburbia is where the developer bulldozes out the trees, then names
the streets after them.
- Bill Vaughan