Bad service

I bought a oven and hob set in August I did notice after some time the plates were changing colour but just thought it's dirt after a few months now is 3months past I realized that the plates are rusting I have been in contact with the online team aswell as the service manager which is quiet annoying as she does not even return emails I asked them for a refund or an exchange but I stil have not got any feedback...I would like to know what steps do I take further as I'm not going to accept an old stove