First, you need to gather facts. Have a quick, professional 1-on-1 chat with each person who appears to show negative attitude toward you or make fun of you. Tell them you have noticed what appears to be impolite attitude/behavior on their part toward you and ask them if your perception is correct and if so, what is causing it, or if you have done anything to cause it.
Document their responses with a date and time of conversation and as precise notes of specifically what you asked and what they replied as possible.
Also, start a journal (keep it private and secure!) of these behaviors on the part of others. Make sure to document date/time and location, who, what, and how.
Once you have a record which demonstrates a recurring pattern of negative attitude or behavior over some time (say, 1-2 months), done one of the following:
- Study company policy about workplace conduct. I am sure there are policies in place which require professional, courteous, polite behavior among employees. There may be some kind of 'zero tolerance' policy regarding hate/abuse etc. Keep in mind, psychological abuse is a form of violence and is most definitely against official company policy for employee conduct.
With policy and your documented notes in hand, schedule a meeting with your manager, provide this information, and explain that this is only the recent fraction of a much longer-term pattern which you feel is creating a negative/toxic work environment and impacting your well-being and job performance.
Tell the manager you feel strongly that you are experiencing what amounts to a form of verbal/psychological abuse which violates company policy. Request immediate corrective action to remedy this situation.
Make sure to convey that you are very serious about this and will escalate and consider legal action unless this is addressed promptly and effectively. Sometimes you need to light a fire under management's a$$ to get results, and it sounds like that time is long overdue for this situation.
- If there is a union at your workplace that you are a part of, then before you do #1, schedule a meeting with your union representative and have the same discussion you would have had with your manager in #1.
Tell them this must end and that you are looking for support in resolving this situation as quickly and effectively as possible, and that you will escalate this to HR and upper management if needed. Union reps are on your side, and they can and will provide substantial assistance in such situation.
Your goal is for this to end ASAP, so do what it takes. Good luck!