Not sure what do you mean with heading page.
Regarding showing the title twice, I guess you have the options set to display the article title. In the options of that menu item, set article title to Not show.
Other than that, it's possible that your template has overrides for the com_content, that manipulate the output of your article pages.
To identify if this is the case, assign temporary the default Joomla template (protostar) for that menu item and see what you get in the front-end.
It's your template that is doing this. There are template overrides, that are using the browser title of the menu item for the page you are looking and injecting it to the breadcrumbs content block.
I think there should be interesting things happening in your template.
Without knowing how your template is structured, a blind guess is that you might be able to spot the part of code in the template's index.php file, using FTP.
You are looking for the part that is outputting:
If you can spot this part of code, grab it (and a bit of its surroundings +- 3,4 lines) and paste it in your question for further investigation.