Samsung CLP 550 problem

[FlickMay]

Bought one of these laser printers mid Jan and right from the start kept getting message 'Install [colour] toner' or 'Invalid [colour] toner'. Managed to get it to clear and print a page or 2 by re-installing cartridges but had to have engineer visit - he changed all the boards but still printer played up. Beginning of Feb he returned and installed 4 brand new cartidges and for 20 days printer was fine. Day before yesterday the invalid toner message re-appeared and haven't managed to print a thing since. Samsung say they will send engineer again next week but I say the printer is not fit for purpose and should be replaced. They say it's over a month old so won't be replaced. But it hasn't worked for 3 weeks since purchase. Anyone had similar experience with Samsung or this particular printer and what was result? (Also posting in 'Law' topic).