Mask a Text Over a Shape Layer

Duplicate the background, assign your number as an inverted track matte or simply create the number dingbat in a pre-comp with proper transparency in the first place by using the number as a cutout on the circle with Merge Paths in the shape layer or again using track mattes. You may want to read up on some of those basics.

https://helpx.adobe.com/after-effects/using/track-mattes-and-traveling-mattes.html

https://helpx.adobe.com/after-effects/using/shape-attributes-paint-operations-path.html

Mylenium