have (got) (one's) number(redirected from have their number)
have (got) (one's) number
To understand or know someone or something well enough to anticipate what they will do. That team is impossible to beat—they've had our number since 2006! Oh, don't worry, I've got his number—he's a typical brat.
have someone's number
If you have someone's number, you understand what kind of person they are, and so you know how to deal with them. Oh, don't worry — I won't let him cheat me. I've got his number.