How to make client pay for the mould change charge?

This topic is very tough during our work. Our company met a case that client ordered Y PVC pipe fitting mould. In the design stage, send sample pictures with detail required sizes. So we make the part drawing, part 3D and mould 3D design all according these sizes provided by client. But the tragedy happened that after we showed client mould trail samples sizes pictures, client required some other much different sizes. Have to make very big change on the mould to meet the sizes requirement. Later, we improved the mould and make pipe fitting mould trial sample same as per the request. However, the mould improvement charge is too high. Another hand the mistake not crated by our company. So we told the client that your company need to bear the sizes change charge 2500usd. As sizes too much different, mould remade the cnc milling tooling and cnc engraving tooling, and changed the ejection pins position also. The improvement cost is too high. But customer didn’t want to pay for it. And told us there is a new 35sets mould new project, need us to leave a good impress to win the order. Our company discussed this matter, and told customer, they can pay us the mould improvement charge 2500usd first, and we can refund this payment into the new order. Unfortunately customer didn’t agree on this. At last, we said not all the change is free. If the mistake is because of us, we will modify the mould freely. Another thing, if the improvement cost is low, then we can make it for client free. Now if we didn’t charge the improvement, your company management will not care about the part sizes again. So even 35 sets moulds placed to us, if this issue happen again on them, we will get hug lost, not earn money.

What do you think? Have we made right decision?