mlewis, you have been taken in by the same con trick used by A's....promises and pleas for help leading to where you suddenly find you are in a deep hole. Then come the abuse and threats....anything to keep you bewildered and at their mercy.
Stop it all, right now.
For me, first...I would get legal advice regarding where you stand in doing his work.
Next I would go to the Dean and lay it all out for them, explaining how you were sucked in to it from the first, how it has got to this stage and that though you have refused to continue, he is trying to force you to do so.
If you have been doing your own work well, then you have not breached your contract and have been entitled to any monies you received as a student.
He, on the other hand is in deep s**t, as he has taken monies he was never entitled to and must answer to that, probably have to repay it all and cop some legal penalty.
What penalty, if any is to be levied on you, I do not know, BUT it could not be anything worse than being worked into the ground as you have been, and now being further abused by this useless, brainless jerk.
Cut contact with him immediately, and let him know that if he gives you any more trouble or threats, you will be telling University officials about the work you did for him, and the police regarding his menaces and threatening behavior.
Get your mum in the picture, as you need her love and support at this time. Frankly, if you were my girl in this mess, I swear your ex-creep would be in too much pain to move, let alone menace you.
Above all, don't pay out on yourself for being sucked in by him, as there are millions of us "smart" women who have been caught up in an A's whirlpool of c**p. Some of us lasted even longer, enmeshed with our losers and took years to wake up and get free.
God bless