It is nothing to do with the 6mm cable - is it a split phase cooker? (i.e. was there a second live terminal?) If so that needs linking in to the supply too, sometimes there is a link in the bag of giblets, sometiles an offcut of wire is needed.
Otherwise its a fault in the hob itself.
obviously its getting power to the cooker otherwise the back rings wouldnt work. double check there are no live connections on the cooker what arent connected. if there is, connect it. if not then it sounds as tho the cooker is faulty
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