My ex has an outstanding balance over $10,000 on my credit card. Initially the interest rate was something like 7.9% but his constant late payments have increased the interest rate to 29.3% and now he can't pay at all. Can the credit card company do something to reduce the balance or reduce the interest rate and future payments or anything else if I tell the credit card company I'll be paying the bill?

Doubtful.

As far as the credit card company is concerned, if the card is only in your name, you are the one responsible for the delinquent payments, and the current rate and balance.

Telling them that your ex made the charges, and was making the late payments is not going to matter.

You might want to inquire as to the policy of reducing the rate, based upon a certain number of on time payments.

That may or may not be an available option.

To go along with what prog said, there's a chance that the cred card company may be willing to settle.