Bad service

I’ve been servicing my mini with Car service city since I’ve had it. Always had the beste service with them. From the lady that does the bookings, to guys that works on my car. The last time they worked on my car was the end of Jan 2020. On the 15th of May i took my car in for some new tyres. I’ve been meaning to do it, but because of the lockdown i had to wait till now. At the tyre centre they told me that my locknut key wasn’t in my car. And one of my tyres is also missing a locknut. I was shocked and went back immediately to car service centre since they where the last people to work on my car. As a lady those r the last things i would check. And i like a said I’ve never had a problem with CSC. When i got there i told them what my problem was, and why i came back to them specifically. The took my car, pulled it in the service centre, according to the guy he wanted to look for the locknut and the locknut key. After a few minutes he came back to me and told me that he can’t find my locknut and locknut key in my car or in their workshop. I asked him so what I’m I suppose to do now since they can’t find it. He told me that i should bring my car back the next day and that he will make a plan for me. I didn’t go back the sat, since i was working. I phoned them and asked the guy that i was dealing with if he had came up with the so called “plan” He then told me that there is nothing that they can do for me since they can’t find my stuff in their workshop, and that he’s sorry. I wasn’t happy at all since i was told the previous day that they would help me. I was close to tears then dropped the ph. I phoned back after I’ve cooled down to ask for their head office’s number. The guy i spoke to told me he’s the owner of the service centre. I should look for the number on their website. The head office will anyway tell me what they’ve told. He was not very helpful at all. Basically telling me I should look for the number myself. I did some searching and i found out a locknut and a locknut key will be round about 400 to 800. I can buy anytime, but I’m just really ****ed at the way they treated me. I dont even know how a locknut key looks like. I’ve never changed a tyre in my life, and I’m the only one driving my car. If it was male I’m sure they would have treated him much better.