*********** Mechanics taking advantage of woman

I took my car to the company (my zone service centre in orchards)last year 16 November for diagnoses they made me pay for diagnoses testing 2x of which showed minor problem the mechanic said he is going to look into the Engen maybe that is were the problem is he dismantled it and said maybe the throttle body is the problem just assuming. fine so he said he has a supplier that has 2 of these parts but 2nd hand throttle body in very good condition for a quote of 5200 I agreed for them to do the work he never spoke about warranty of which now they told me is 7 days but before the 7 days only 2 days after they worked on my car I brought it back to them coz it was worse, they looked into it and told me that I must drive my car maybe it's because it was standing for long time of which I did but still I experienced same promblem. I went back to them within the 7 day warranty of which they told me no it's something else that is problem it's 2 months now I left the car with them they now telling me I must pay for another throttle body when the one they put in is faulty. I asked them to reimburse my money they refusing they saying they going to put the old one and they done with me. I need help these people are ******. Nissan Micra