Brand new printer

I purchased a brand new Canon printer from Matrix in Northmead Benoni, firstly the staff there are all children and not very helpful. They employee that assisted me was full of glitter and said he had a hell of a night the night before (not very professional) then we took the printer and he never said we must purchase a USB cable so I had to go back the next day. (time and petrol wasted). Now I have this printer the first cartridge is finished after printing +- 30 pages so I replaced the cartridges with the new ones I got with the printer and printed 12 pages now (only black and white writing) and now its finished again. This was not a cheap exercise so please explain to me what is happening? I am running a business form home so its costing me time and money to worry about a printer that does not work and only print 12 pages.