Maria
It's actually quite unusual for an ESA113 to be issued, there is no legal requirement for those assessing you to contact your health care contacts.
I'm afraid you can't insist that your GP write a letter or report, it's entirely up to them. Some GP's use the forms as an excuse not to provide assistance with benefits and others genuinely believe that the DWP will contact them if they need information.
Assuming you can afford it, you can try offering to pay for a report, but if you go this way make sure you understand what you are getting, you don't want to pay for something that is actually of little use.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems