Most of the time when you try to override a component but your changes don’t seem to apply is because the overridden component content isn’t wrapped in a root element.
For instance, this is valid:
<billing section="top"> <div> <p>Test</p> <p>Test 2</p> </div> </billing>
But, this is invalid:
<billing section="top"> <p>Test</p> <p>Test 2</p> </billing>
We output an error in the console when that’s the case, so this is the first thing you should check: