Whilst it is frustrating dealing with the IHG when there are issues, their T&Cs pretty much say they can boot you out for whatever reason.
Membership Cancellation. SCH reserves the right to cancel any IHG® Rewards Club membership and revoke any and all unredeemed IHG® Rewards Club points collected by any member for reasons that include, but are not limited to: 1) violation of these Terms and Conditions; 2) misrepresentation of any information or any misuse of this Program; 3) violation of any national, state or local law or regulation in connection with the use of membership privileges; 4) failure to pay for hotel charges; 5) a check to a participating hotel brand that is returned for insufficient funds or is invalid for any reason; 6) commission of fraud or abuse involving any portion of this Program; 7) more than one active account per member; or 8) physical, verbal, or written abuse of hotel or IHG personnel; or 9) action, in any other way, to the detriment of the Program or any of its alliances; all as may be determined by SCH in its sole discretion.
However, I think you've already admitted your 'crime' :
The only thing I could think of is booking hotel for friends and family but that's nothing illegal?
Certainly not illegal, but having someone else use your IHG account for their stays would have you fall foul of 1, 2, 6 and 9.
There is a specific allowance for US and Canada hotels whereby points can be earned on up to 9 rooms providing they are all booked by the account holder, and that the account holder is also part of the group staying at the hotel.
If you can prove (and unfortunately the burden falls on you, not IHG) that each stay on your account was used by yourself, and each stay on your GFs account was used by her, you should be able get the account reinstated and the points back. But prepared for a long process.