Proverb: quit a habit

What proverb in English means that people get rid of old habits hard? (if there are any)

An appropriate idiom would be "Old habits die hard".
"An old dog will learn no tricks." is a proverb and is a lesser used form of "you can't teach an old dog new tricks."

It is impossible to change people's habits, traits or mindset.

Source: Wiktionary and Know Your Phrase

Depending on the context a leopard can't change its spots may be appropriate.

This proverb means that despite all efforts (or advice), a person will revert back to their old self (habits). It is usually used when referring to bad habits.

This idiom comes from the Old Testament (Jer. 13:23). The Hebrew prophet Jeremiah tries to persuade an evil shepherdess to become good but when he realises that it is impossible to convince her, he says: “Can the Ethiopian change his skin, or the leopard his spots?”

From: bloomsbury international

How about this?

A dog's tail can never be straightened.