While nothing will defeat someone's free will -- at the very least, if there were something that may, not many people here would suggest it -- there may be some things to help.
Your most common suggestion will be a honey jar spell. There are many threads about it here. It is a spell built around a jar of honey loaded with items associated between you and the other person. It is meant to 'sweeten' emotions between the people, and is in many people's opinions a decent option because it will not cause love to occur or rekindle, but it may soften a harsh relationship.
That said, you ask as if your ex is completely out of your life. There would be nothing wrong with also doing a 'think of me' work as well, after letting the honey jar work for a while. If you have lost contact with this person, it may be a way to inspire them to contact you.