I've written to companies in the UK before with similar deadlines, it can be statutory - I am giving you notice that this communication starts the clock on the 30 day period I am required to allow you to give me a satisfactory resolution before I will escalate this case to the relevant authority.
Last time I had to use that sort of language was with a deranged ISP who had failed to deliver an internet connection, then decided to chase a debt for unpaid bills for this non-existent connection two years later.
This was Bulldog Broadband, back in the mid 00s when they were about the first to advertise 8Mbit in London at a relatively reasonable price, but were then swamped with orders and couldn't seem to even keep track of what they were doing, let alone deliver anything.
But you're right it could be any one of a number of them! I had problems with quite a few over the years.
Among the amusing misfeatures of bulldog broadband was their cancellation process, which required confirming by sending an email to "cancellationconfirmation@..."
Said cancellation confirmation address had not been set up and would just bounce.
Last time I had to use that sort of language was with a deranged ISP who had failed to deliver an internet connection, then decided to chase a debt for unpaid bills for this non-existent connection two years later.