Custodial parent relocated and child decided to stay behind so I now have 75% custody. do I have to pay travel expenses

Child support is calculated based on the parent's timeshare with the child and the income of each parent. You are entitled to file for a modification of the child support order, since there has been a substantial change of circumstances (due to mother's move, you have become the primary custodial parent). If the Department of Child Support Services is already involved, contact them. If not, file for a modification. If your incomes have not changed, then your support obligation will decrease and the obligation may even be shifted to the mother to pay you.

As for the travel expenses, many times the court will charge the parent that moved away with 100% of the travel expenses for at least the first year, but not always. After reviewing the case, the court will make an equitable allocation of the travel costs for visitation, depending on the income of the parents.

It is your responsibility to obtain a new (modified) order. Until you do, the mother's contention that you owe under the existing order is the rule of law and you could be found in contempt of court for failure to pay as directed. Please consult with an experienced Family Law attorney to get more information.