Bad service and Violation of Consumer rights

I purchased a caliper for my Audi A1 2012 5 doors, upon purchase the wrong part of the caliper was given to me I only realized when I went to the mechanic to fix, then I went back to exchange the part I was told to return the following day for the right part as they would have it ready for me in the morning, I went back the next day only to find the person who promised to help me was actually on leave and the part was not ready as promised I waited for what was about 20 minutes as they promised someone was on the job after realizing that no one was attending to me I started complaining and that’s when they started to search for what I was looking for and after about 30-40 minutes they gave me a part , I did mention to them that the part looked bigger as compared to mine but they assured me it was the one. The same day I went to the mechanic to install the part and as I had said it was bigger and I communicated this to them and sent a picture again they promised to get the right part and that I should come the next day, they advised that they want to actually have my car and see as sample, that’s when I proposed to see them 2 days after (on Saturday) as during weekdays it would mean leaving my car there with no knowledge of what they do. Saturday morning i.e. 30th of April 2016 I contacted them and told them I was no longer interested and that I want my refund they then told me that only their boss can process a refund and that he wasn’t in and he would only be in the coming Tuesday I told them it was fine and that I would come on that day , that’s when they told me they had mistakenly given me a caliper for a 2 door they said that a 3 door caliper is different from a 5 door one they then promised to get back to me and that I must fetch it by 11AM that day when I tried contacting the guy helping me by 11 AM I was told he was busy and that he would get back to me but he never did and never rep**** to my messages on the mobile phone. On Tuesday the 05th of May 2016 when I messaged them to alert them that I would be coming for the refund they then tell me about the 21 working days waiting period for a refund and when I get to their offices they also tell me about the 20 % handling fee interest, when I checked the slip I saw a mention of the 20% but no 21 working days waiting period I filled a refund form but I noted that I do not agree to the 20 % handling fee this is because I feel it’s unreasonable because they failed to provide me with the services they promised and adding the 21 days is extreme I am filling this complaint because I do not agree with the 21 working days period and 20% handling fee I feel it’s in violation of my consumer rights since they are the ones who failed to provide services.