Page Setting will not apply to page

I have a page which I have set to PHP but the output while viewing in browser it reverts to HTML whereas other pages set to PHP do not.
Code had inserted previously inserted for the page is being added at the base of the page.
For the life of me I can’t find why and from where it is being inserted.
It doesn’t have a tag but it is included after the </-- Main container END --> line and before the