I have recently left my partner and moved out. I am still paying my share of the rent for the apartment and also my share at another apartment. I moved out a month ago. My ex has found a new roommate yet says i still have to pay my share. The roommate they have now is not on the lease. What should i do continue paying or quit?

You gave notice. She mitigated damages finding a new roommate. That should be the end of it. To ask you to keep paying now, unless there is a lease or contract obligating you to, or unless it is for unpaid shares of utilities or something like that seems wrong. I suggest that you tell her you are done paying and you may want to ask an attorney to ask write a cease and desist letter to her because this might border on extortion if it keeps up.