True Story -
Was being blackmailed by my ex for more money or she would stop me seeing my son - went to the court office in Dun Laoghaire to set a date to have the maintenance regulated by the court - was told only the mother could apply for maintenance!
Given that there is none in place, stop paying her anything at all the minute she seeks to interfere with access.
Also, do you have a current court ordered access agreement? It's not worth the paper it's written on, but you should get one if you don't have one nonetheless.