Bad service

I bought a phone on Saturday at pep home Jabulani mall a V41 and it was never explained that the phone is extremely slow can't even download any applications when I take it back I'm told they can't exchange as it's not a technical issue or broken its just slow and vodacom is alsp aware of the fact I ask why they keep selling it they say Vodacom keep bringing it and they want it sold I'm very disappointed please help