Bit of advice re misdescription of goods. We bought item due to description, shop nowchanged it totally. What rights do we have?

[Piffle]

briefly
Bought induction hob sold as no zone place a pan anywhere for flexible cooking. Bought as wanted option of 5-6 pans for Xmas etc
Turns out when we installed it the hob has 4zones only no more...
The shop have since changed the blurb saying it is 4 zone hob.
They sell another 4 zone hob for 40% less then we paid( we paid more only for flexibility)
Given that what wouldbe appropriate action?
Fwiw they have offered half of the 40% pricedifference in a voucher for their shop.
I have never had to deal with this sort of thing before?
This was part of an entire kitchen with appliances that we bought from them btw

only issue with rejecting the item is that we very expensive worktops cut to fit that hob, so to reject it would mean replacing all of that as it is bonded.
Eeeks
thanks though, if we strike problems rejecting their offer I'll look into that organisation.

Link to website:-

www.consumerdirect.gov.uk

thanks have had a read now...
i will email them I think for guidance!