Neck Harness and Neck and Spine Pain ?

I started training my neck a while back and got pretty strong, i eventually did 20kg for 2 sets of 50.

stopped that since my neck and spine are killing me, i can’t barley move my neck backwards or forwards without some sort of pain and my thoracic spine is hurting me too.

What should i do ?

I’m having a hard time believing this is a real complaint.