How do I get a Spanish child maintenance order adjusted as visiting order has changed?

My Ex wife lives now in England, we lived in Spain, and has taken the spanish visiting order to court and got it changed via english courts without me being able to defend myself. I now have to pay all trips to see my son. She wants the spanish maintanence order to stay the same as it is more than the CSA say I should pay under normal circumstances. I can not afford to pay for everything. I am paying according to the CSA, but she is saying that I cannot see my son unless I pay the Spanish agreement. How do I get the order changed in England so that she will stop blackmailing me and let me see my son?