DUWO doest not want to return money after contract termination.

I get the contract through the direct offer from VU and I wanted to move out but to be able to move out I needed someone to take over the agreement , who meets condition of being enrolled in higher education in region of amsterdam.I did find somebody like that. DUWO on multiple occasition assured me that my contract ends on 15. june and that other person signed the contract, and that my money will be refunded but they gave me my contract back to continue till 16 th of august after being terminated and keeping my money. I was notified of this that the other person did not signed or paid on 25th even though I had nothing to do with agency anymore after my contract termination .
Thank you for your help
Kind regards