No customer service at all

In Dec2018 i bought a totem 29inch bike for R2000 for my son as a gift, After only 5months the derailer breaks and i send it back to the store for repairs only to be charged R500 again to have it fixed. After recieving the bike a month later the same derailer breaks and is told again to pay R500 which i am not prepard to do sothat it can break a month later again, after it broke the second time my son actual got hurt falling because of the part breaking into he's chain. I contacted a pro bike shop only for them to tell me u cannot just the derailer, but the chain and the cogs to, its like changing a cars oil without a new filter. Please help, worst service at makro after thinking very highly of them and buying lots of expensive items from them