Can't login because phone number changed

I changed my phone number, but when i did, i forgot to change my phone number in-game. I’ve already changed my password, but i need to use my old phone number to verify my identity to be able to log back into Halo MCC. I’ve already tried calling Microsoft and I’ve explained the problem to them and they said that it’s not their problem, it’s Halo’s problem. So is this a Halo problem or is this a Microsoft problem?

This isn’t anything to do with Halo or 343 I’m afraid. MCC uses the Microsoft account that is tied to your Xbox Live gamertag, if for any reason you have issues logging into your account it would be Microsoft Support you’d need to reach out to. I imagine when you mentioned it being related to MCC, that’s why MS support would direct you here.

If there is no other way for you to verify your account other than using your phone, you may be out of luck. Always best to make sure you have a backup source like email or something that you can use. I would try logging in here and see if there’s any way you can verify by email or something:

Short of that, seeing if there’s any way you can get your old number on to a new, additional sim until you can swap it over. Would need to check with your cell provider to see if that’s possible