Unknown error on contact form plugin…

Hi everybody,
I have been trying to create my own plugin for the past week and a half. I didn’t find it particularly hard but I have been stuck for the past couple days with an “error”.

Basically I am creating a contact form plugin. The form’s action is the page itself (I used get_permalink()). Everytime I submit the form, if the form is empty, the page is just reloaded, normal behaviour. However, if enter anything in the form and then click the submit button, the page is reloaded but nothing is displayed in place of the form; The header and footer are here but the form itself is not here… I have been trying to debug this for almost a week now and I just don’t know what the problem might be…

Can someone please help me find what I might be doing wrong?

There is a copy of the code on Bitbucket (https://bitbucket.org/azizlight/wp-useless-contact-form/src/) and there is a working (not quite..) copy here: https://uselessgeek.com/youjiii/wordpress/ucf/