You're using a select subset of many definitions for figure, number, and digit.

A [digit](https://www.merriam-webster.com/dictionary/digit) is a single numeral (0-9), like the digit **5** in the number **5**, or the digit **5** in the number **2507**.

A [number](https://www.merriam-webster.com/dictionary/number) can have one or more digits, like **7** or **2507** or **2,507.38**.

A [figure](https://www.merriam-webster.com/dictionary/figure) can be a shape, a diagram, or a number; if used to describe a number, it can be composed of a single digit or of multiple digits.