Opportunistic billing

I had curtesey vehicle outsourced from them and they were supposed to fetch it on a Saturday. I called their branch, their head office and even the insurance broker for them to come and colled as it was due for collection. The head office responded to say they will contact me back and never did. Subsequently they came on a Monday and I was told that they were fully booked on Saturday that is why they could not come and now they are billing me for the two day. I have proof of calls and emails on the day and they still want to bill me for this. They are nothing short of ****mers