ZRB23200WA Zanussi fridge-freezer fridge compartment too warm?

I have a ZRB23200WA Zanussi fridge freezer purchased March 2015 (so not that old). The freezer works perfectly and has no ice build up (so no air flow issues). The fridge on the other hand has stopped getting cold. I've tried setting the slider to the min setting which the manual indicates that will provide most cooling to fridge (vs freezer). It seems the fridge just won't get cold - any ideas?