There's a firm ball under my jaw that's been there for over two years (hasn't changed) doctors always say swollen gland.. is it most likely a tumour?

Probably not: If it starts to change, get bigger or become painful follow up with your doctor for a re-check.

Otolaryngologist: This may be an enlarged salivary gland or lymph gland. The fact that hasn't changed in 2 years is reassuring. However, for peace of mind an otolaryngologist should examine, advise and follow you,unless he/she states otherwise, for this growth even though it appears benign.