I have close to 20000 pages on my main account, and have always had more than 10000 pages for the past 10-11 months on that account, and have not been banned. Are you sure that it is the pages that got you banned, and not a full marks/house pride? Because JC usually don't give a reason for bans other than "you are using a modded client".
I remember that a few people were speculating whether buying pages or converting pages would get you auto banned a few years back, and a few people seemed to think so. However after checking the dates that the comments were posted, most of them coincided with full marks events. It's possible that under a manual inspection from JC that high pages will get you banned, but otherwise I don't personally think that there is an automatic check for pages in the same way that there's a check for 600 or more energy on accounts that haven't spent real money.
