For future reference...

I spoke to someone with thanks to Claire's doc. Then hsbc logic kicked in:

You *can't* request a new card over the phone if yours is faulty. You need to print out a replacement card form, fill it in, take it to a branch and get your signature verified. The branch will then arrange to send you a new card.

However.

You *can* request a new card over the phone if yours is lost. They will ask you some security questions to verify your identity then send you a new card.

The reason? A lost card is an emergency. A faulty card isn't.

So, don't tell them it's faulty, tell them it's lost.