i got removed from xbox ambassadors program without an explanation

You'll want to email xboxambs @ microsoft.com (remove the spaces) to contact Ambassador staff. Keep in mind, you can be removed if you were given an enforcement action.

There was also an issue recently with the background check for the program. If you previously had an enforcement action but joined the program before it had been 1 year from that action, you would have been removed and will be able to rejoin after it has been 1 year from that action.

You'll need to email xboxambs @ microsoft.com (remove the spaces) to contact Ambassador staff.

You're not the chap that UnyoBro said got banned recently are you or it might have something to do with your gamertag.

You need to send an email to xboxambassadors@microsoft.com for more information. No one here can help you, sorry.

One of the requirements for being in the program is that you cannot have any enforcement actions on your account. Unless the rules are changed in the future, you would not be able to reapply.