sorry for the late reply
no,i dont think paying JC with muggles money gives you immunity from being banned. (having said that, on another game (not HPHM ) i did pay real money and the account was not banned even though they must have known i was cheating )
as for how i was banned..to make a long story short. i was at year 7 and the last chapter ( at that time ) was doing an assignment for Amos Diggory ( the man is a bad omen, he got his own son killed because he is such a bad luck, no wonder my account banned dealing with him haha ) so anyway, the mission got stuck. i complete it but it glitched and not register as complete ( i trayed every solution any one could think of..i even waited for a whole month on the hope the new game update will correct the issue. no luck . so i contacted JC to ask them to finish the assignment manually for me ( a procedure they gladly do for any non naughty player ) i knew when i contacted them that 99.9% chance i will get banned,,,and yes they were up to my expectations :)