repairs

I purchased a sewing machine for R1999 at HiFi corp in Jabulani on the 30th August 2018, the needle of the machine got loose within 30 days of purchase.I took the machine back to the shop because it still had warrant, and I waited for over 21 days to get feedback, on the 3rd of November I went to the store to check if it was fixed but was advised that the machine was damaged because I used cooking oil which I found to be an insult,how can I use cooking oil on a new machine, just a month after purchasing the machine, now they are telling me to pay over R1500 to get the machine repair. I have waited for over a month now to get the machine back and I want this to be sorted urgently