car is falling apart

I bought a pre-owned mazda 2 at McCarthy Wonderboom in August 2014,firstly when i got the car the handle on the back sit door fell off,then they came collected the car and fixed that. Then when i got the car back, i wanted to pour petrol then i realised that the pin to open the petrol tank was broken, i reported that but was told that they will order the part to fix the petrol tank door then i can get it fixed myself. I received the part to fix the petrol tank door but don't understand why i must spend my money to get it fitted. then in december 2014 the battery died, i had to get a new battery.Now yesterday the electronic key stopped working and the car wouldn't open,i then called my brother to bring the spare keys however the spare keys do not work. So i was stuck for an hour waiting for a lock smith to help me open a car that has a spare key which does not work.I know the car is pre-owned bit surely before the sell it all this technical issues shoul be looked.I am a woma that is why when i needed a pre-owned vehicle i bought it from a dealership instead of a s****yard,however at the rate the car is falling apart i might as well have bought it at the s****yard.