Can't change my phone number in Mac App Store

Thank you for the reply.

No, it is the same Apple ID. I'm sorry I didn't clarify that. I entered the same credentials at account.apple.com and in the App Store, and it displayed the same email address (associated with my Apple ID) at both places—but different phone numbers.

I managed to solve the problem in an odd way. In addition to a fairly new iMac and Mac Book Air, both of which I use regularly, I still have an old MacBook Pro running an old version of Mac OS. I logged in on that old computer and initially saw the same problem: the App Store displayed the outdated phone number. But that old version of the App Store application, unlike the current version, allowed me to edit the phone number. So I changed it, and now the correct phone number displays in the App Store on my newer computers as well.

So in a sense the problem is solved, but I'm still mystified about why it happened in the first place. It seems the App Store doesn't take personal information from my Apple ID but maintains it separately somehow.

Thank you for the suggestion—but I don't see how there could be two separate accounts involved. As far as I know, I have had only one Apple ID account in my life. I did change the email address associated with my Apple ID at one point, but that's not the issue: the discrepancy I've observed involves only the phone number that shows up in my personal information, not my email address, and I don't use my phone number to log in.

In any case, I logged into account.apple.com and the App Store using precisely the same email address and password, on a total of three different Mac computers. On all three machines, I saw different phone numbers appearing in the two places (until I finally managed to change the outdated phone number that appeared in the App Store).