There have now been many instances customers sims being hijacked and their bank accounts being emptied. I don't know if any of these have happened to GG customers, but because of the recent TSB fiasco it's highlighted the worry that if it does happen you will need the quickest way possible to disable your sim. As GG runs on the community there is no-one to call to do this.
My suggestion is as follows
1. Assuming you can still log in to your account I'd like to see the option to set up a secondary password (originally chosen and not possible to change online unless you know the original answer) which allows an immediate sim block 'button so the quickest blocking can be instigated.
2. If your account has also been compromised so you can no longer log in, I suggest a general Sim block reporting page where no login is required as such but entering your telephone number and answering perhaps 2 security questions for which you have previously given answers (originally chosen and not possible to change online unless you know the original answers, and one could be the special blocking password chosen above), would then allow rapid blocking of the sim.
I appreciate none of the above will guarantee that the thieves haven't already emptied your bank account, but the faster you can block the sim the more chance you have of prevention.
I would also say that at this stage it isn't clear how the thieves are managing to log into the bank accounts and make payments after they've hijacked the sims. No doubt there are other security issues here, the sim card hijacking is just one part of the problem; neither am I suggesting that GG is insecure in this regard.