How hard is it to stop using cocaine?

The key-Word there is 'habit'. Me personally, I do not believe in addiction or at least addiction to do with psychological narcotics / other habits.
Unlike heroin which after habitual use becomes bodily addictive, that is your body 'needs' it to function properly cocaine is not like that, and is all in the individuals mind.
Psychological.

To overcome a cocaine habit can be very difficult not least because it feels good using it.
I used for a couple of years but it got the better of personal relations and began causing issues. Staying away from it at the start was difficult and it took me a couple of attempts to quit. The key was really that I didn't 'want' to quit.
The person must 'want' to quit.

Delete contacts, stay away from persons or situations where the drug may be, a change of lifestyle and a will to not want to use again is necessary.

It is all in the person's mind.