This seems related to the previous issue you were having with your host where Prepared Statements aren't working. I'm not sure why.
I updated the queryobj.php file and added a parameter for turning off Prepared Statements. That is on line 26. And then I updated yours so that Prepared statements are turned off and the insert works now.
I also created a page debug.php that has the simplest Prepared Statement that should do an insert, but it is blank. You can show that page to your hosting provider if you want and maybe they can help debug why it isn't working.
Please download the updated queryobj.php file so you have a copy where it allows you to turn off Prepared Statements since your local version is now old.