All breakup endings go a little crazy. The people involved usually go through a personality change. Usually, couples involved in the breakup react different to the end of the relationship. One of the might try to keep the relationship alive while the other just wants to move on with their life. The one giving the "my ex is ignoring me" is usually the one who still wants to make the relationship work.
It’s quite normal for your ex to act coldly towards you even after an amicable breakup.

There are different reasons why your ex may not want to talk to you. Your ex could be ignoring you because the relationship ended just a few days or weeks ago. Chances are your ex is already trying to move on with their life. What they want to do right now is forget the pain caused by the breakup.

Ideally, you should be doing the same thing.
Your ex might still have feelings for you and that is why they’re ignoring you. It's possible they are still in trying to get over the break up. The breakup caused them more pain than they care to admit. This kind of feeling is often felt by those who still want the relationship but know how to make it possible. Your ex probably thinks that there's no hope of getting back together and therefore chooses to ignore you.
In situations like this, it is best if you leave your ex alone.
Sometimes, your ex will start to ignore you even after the two of you have established friendship after break up. This kind of behavior can be explained by several things. They might be experiencing personal problems in which case, you are not responsible for it.

Your ex might want to concentrate on the problem and solve without involving you. If this is the case then you should be thankful.
Another reason for why your ex refuses to talk to you could be because your ex is already dating someone else. Now that they have a new partner, it would be awkward to keep on seeing you at a regular basis, right? If this is the case then you should give your ex some space.

Your ex might also be choosing to overlook you because of other reasons. It's possible that your ex just doesn't want to communicate with you anymore. Perhaps you didn't perform well as a boyfriend or girlfriend, you were mean to them or you just weren't fun to be with. If this is their reason for ignoring you, don't get mad. Instead, understand them and learn from the situation. Use this to become someone better for your next partner.

Author's Bio: 

Do you want to know the signs your ex still wants you , you might be interested in checking out Avoiding a Breakup to save your relationship.