Custody and child payments

Hi, I have a problem. My son is five and a half years old. And I’ve been divorced for five years. His mum wouldn’t accept joint custody. She insisted I take him and pay for everything or she would fight for his custody and win, because she is Taiwanese. I was new here at the time and agreed. We divorced because I wouldn’t give her my salary every month… she’d written a contract that stated I’d have given her all of my money every month. I refused and she divorced me inside 3 days.

Anyway, for his whole life I’ve paid for everything… education, health care, clothing etc. and he’s lived with me five days per week as a single father and stayed with his mother’s family on weekends for his whole five years of life.

In February as a group we decided that he is better off staying with my ex wife’s family 4-5 days per week and with me the remaining days because it’s incredibly hard for me to juggle work, childcare and life as a one man army.

However now his mother’s family are asking me for $12,000 per month for food and collecting him from kindergarten. This is on top of his $10,000 per month kindergarten fees, medical fees etc etc. his mum said if I don’t pay, they won’t care for him anymore and I’ll have to quit work to be with him or pay a nanny which is more expensive. I’d like to renegotiate his custody, and also make her finally contribute something financial to his life. What can I do?