why i can’t buy UC game with sim card

Follow the information that Idris has provided. You can also check with your cellular provider and see if they support iTunes and App Store purchases through your cellular account. See this, Availability of mobile phone billing as an Apple ID payment method - Apple Support

Not all cellular providers support making purchases with your cellular account. That would be up to your carrier.

Start here:

Payment methods that you can use with your Apple ID - Apple Support

Change, add, or remove Apple ID payment methods - Apple Support