Collection is not the head, although it is a common misconception (for which I blame the term "on the bit"). Head carriage is the final symptom when all other pieces are in place. Research each step of the Scales of Training. I have several posts about it on this website, if you'd like me to link them?

Hi Munther 🙂
I know how difficult it can be! You have to work on a global collection, not just the head, here are many exercices to improve collection for you to try (which helped me a lot) : https://dressagetoday.com/instruction/counter-canter-28686