For anyone else's info that is placed in this situation you need to know...
It is possible to stop payment on a Cashiers Check if you go to the issuing bank and tell them you suspect fraud is involved and this is the only legal way to stop the payment I know of..... You will then sign papers for the bank, the bank will then stop the payment if you were quick enough to beat the check clearing and they will hold your money for about 30 days before returning it in full to you...I have been there done that!!