Use
call mvn clean
call mvn package
Note that you don’t need semicolons in batch files. And the reason why you need to use call is that mvn itself is a batch file and batch files need to call each other with call, otherwise control does not return to the caller.
If you want subsequent commands to echo to the command line (show in batch output), you must also do echo on after the call mvn is done (on the next line). This is because mvn turns echo off and doesn’t turn it back on.