Slurs are derogatory terms weaponised by the oppressor to attack the oppressed. Not the other way around.
Slurs are verbal violence against people's identity and immutable characteristics. They're not just “mean words”. Not every word you don't like is automatically a slur.
Slurs attack a person. That mean word you're crying about on twitter merely (and rightly so) attacked your views.
A minoritised community calling you racist, homophobic, terf or whatever isn't “oppressing you”. They're calling you out. They aren't “hating you”, they're shaming you.
Shaming you into changing your hateful views. Cause you can do that. You can simply stop being an asshole towards trans people, queer people, people of colour, or whichever other minoritised group you've decided to bash today. Nothing bad is gonna happen to you if you just start being a decent human being.
So no, TERF is not a slur. It's an accurate description of your disgusting, hurtful, hateful views.
Stop playing a victim, you bigoted asshole.