I have and am being bullied at work, what can I do about it without having to leave my job?

I work for a large organisation and have for the last 3 years certain colleagues have refused to recongnise my existence and value, they attempt to undermine my position, status, worth, value and potential. Within my team I am treated differently, such as being excluded from what’s going on, ignored, frozen out and sent to Coventry being belittled, being overloaded with work covering I have bought this to my line managers attention many times over the last few years and he acknowledges that yes they do this but to date has done nothing about it. I walked out on Thursday but have decided to go back tomorrow and fight my corner but what exactly are my rights and how do I do it. Ideally I would like to stay but can not with the way things are

Optional Information:
Bury St Edmunds, United Kingdom

Already Tried:
Apprasials and meetings with current manager to deal with the problem he has sympathised but done nothing thought I would ask for a meeting with my managers manager, HR, myself and a colleague I work directly with - I have discussed with the 3 outbased staff I work directly with and all support whatever decision i make 100%