Job reversed final pay deposit and Are withholding it until I help train for free?

My old job is harassing me via email and LinkedIn nonstop. The HR manager as well as my previous manager reversed my last paycheck and are withholding it until I train the new employee for free. They say that I am obligated to transfer all knowledge and information upon my departure. I have trained the new employee for three weeks Straight and the information is still not sticking. I have even recorded hours of training via screen share. Somehow they lost the training videos when going through my files after receiving my laptop and are requiring me to redo them without pay. To add salt to the injury, this newly hired employee was given a higher title for my same job and is being paid more than double what my previous salary was. They are harassing me via email distracting you from my new job and they refused to give me my final pay causing me to be late on my rent. After all I’ve done for this company, now they are deciding to jerk me around and this is burning me up. What should I do?