But I no longer own that number.
And from the customer Q&A forum, I realized I was not the only one - it is almost impossible to find an actual human from Facebook to solve this kind of verification problem.
All I wanted is to delete it, but I can't. Now, my account becomes a zombie, can't be used, can't be deleted, and has lots of personal information. All thanks to the falsehoods Facebook programmers believed about phone numbers, and its non-existent "customer [0]" service.
I've heard Google has similar issues [1], if the machine works, then everything is fine, until you need a human...
Repeat after me: fxxk Facebook.
[0] because I'm the product, not the customer?
[1] https://news.ycombinator.com/item?id=18886804,
and read this comment, https://news.ycombinator.com/item?id=18887548