Your parents are obeying the dictates of the Faithful and Wise Servant. Association with you will violate Jehovah's instruction and therefore compromise their chances of surviving Armageddon.
They will be permitted to stop shunning you only when you crawl back to Jehovah. Any chance for you to be accepted by your parents before that happens is nil unless, of course, they see what they don't want to see...that their religion is a sham.
My advice is to stand strong and honor their decision to shun you. Your strong stand to avoid contact with them as requested may help them to eventually see the real problem. There is never a reason to beg for acceptance or love or pity. Commit theirs and your situation to God and be strong until they are ready to come to you.