These sounds are hard because larynx needs to quickly close and open to pronounce them and the following vowels correctly, while our larynx gets easily stuck in closed position, hence the blocks. You can try practicing these slightly mispronounced by adding a humming h-sound before the following vowel, like that: c(h)at instead of cat, dhog instead of dog etc. Continous airflow and light connection when tongue touches the roof of your mouth avoids the deadlock of larynx fully closing and the refusing to open again. Try reading some pages from a book out loud every day (ideally to a listener, i practice with my children or a bot) when using this technique. Hope this helps!