unhappy with cellphone its more for 12 year old

went to the shop on 21/9/15 to buy mtn phone just to receive calls and sent sms the guy who was on duty told me why not take nokia of R478.80 i already have phone which i also bought there and is working perfectly i actually wanted a cheaper second phone just to receive mtn calls when i got home tried to load whatapp got message that the network is not supported.when back to the store to exchange the phone for cheaper one because the only reason i took the phone is because i was told it has whatsapp i explain to the unhelpfull unfriendly branch manager who referred me back to the person who sold me the phone which is a waist of time and effort. i would rather have cheaper phone to receive calls then have a phone as expensive as the one i have i will only use occassionaly i want my money back