I have a spare EE PAYG SIM which I was trying to keep the credit on. It came with a Talk&Text "pack" which deducts £1/week. I texted "STOP PACK" to 150 which came back with a "REPLY YES TO CONFIRM". Doing this seems to have no effect....and the Pack always reinstates itself!

Is this correct? You cannot keep an inactive PAYG SIM on EE?

You should be able to register for MyEE online and then deactivate the pack there before topping up (I'm sure I did it with a sim late last year).