New Fridge – not getting particularly cold

bought a Zanussi Fridge (Zanussi ZRG16600WA Larder Fridge) for undercounter – small 55cm wide one for kitchen

basically its not performing great – top shelf averages 8-8.5C at best (sometimes 7 if you leave it overnight shut), middle shelf averages about 5 at best 0 mostly 6

its about 6 weeks old – and its set to max – some ice visible on rear plate

took a look round the back – – radiator fins are pretty hot – some corrosion round the joints on one of the pipes bottom of radiator although this prob just normal from the disimilar metals (or could it be “leaking”)

if I set to “zero” it clicks off – so the dial of the thermostat seems to work

see photo for back of fridge

our old fridge would literally freeze stuff if it was set over about half

we’ve been told we’ll be charged a call-out charge if found to be not faulty

interestingly the manual states minimum of 10cm gap at top betwen fridge and counter, but John Lewis website (where we bought if from) – states minimum 2.5cm all round (which we’ve got)

thanks for any help or suggestions – it was only a cheap fridge (150 new) – but I’d expect it to at least keep reasonable temps