>>>£4919 for Fuel and Lubrication
That sounds like a really good night in Wetherspoon's to me ;-)
While financial services companies generally do try to monitor purchases, to look out for unusual transactions, there's no way that it could be done manually; they must rely upon their computers. It sounds as if their software needs a bit of tweaking, which may well happen as a result of your complaint.
My usual moan is when I find that a transaction has been blocked as 'unusual' for no obvious reason. (e.g. I had difficulties paying easyJet about £60 for flight tickets because Barclay's computer regarded it as an unusual transaction for me to make!). It can be hard for card providers to get the software exactly right, so that genuinely unusual transactions start alarm bells ringing, without loads of 'false positives' causing annoyance to customers.
To be fair to the card companies though, Santander did spot when someone withdrew £800 out of my account (in three separate transactions over three days) when I'd not used that account for several years and I lived nowhere near to the relevant cash machines. Fortunately, they were just as good about refunding the money to me!