Doesn't the system prevent you from purchasing if you have reached the limit for the year? I can't see Hilton shutting the account down solely because the OP had somehow managed to purchase more points than was allowed if they went through the normal purchasing channel to acquire them.
OP are you able to post a link to the reviews you put online? It may make things a bit clearer if we can actually see what you have written/reviewed.
It's possible that a few of the hotels that you have complained about are all owned or operated by the same company/Franchise. The hotels will be charged a fee by Hilton for handling the complaints and it's possible your name has popped up on the monthly return to Hilton a few times in quick succession and a beancounter has spotted it, raised it with management as a concern and they have duly asked HH to take a look at the account.
Also I'm sure you are aware that your "Worth" as a customer is also tracked by hotel companies. They have CRM systems that are pretty good at calculating how valuable a customer you are etc etc. All the feedback, complaints, compliments, compensation, in-hotel spending etc etc is logged on Hiltons OnQ system. If you are non-profitable or a perpetual complainer you will flag in no time at all whilst Hilton have been known in the past to "Invite customers to stop staying with them" following bouts of perpetual complaining.