"Go online or phone to buy car, home, or pet insurance" is the tagline on their Google search. The catch is right there in plain sight - to buy.
Yes, Direcrt Line will happily take your money on the website, without speaking to anyone, but you cannot later cancel a policy without calling them, presumably to give them the opportunity to put you through a "retention journey" (call-centre speak for 'how do we bully this customer into staying')
The website boasts you can make changes to your cover 24/7 but only some changes clearly, after all cancellation is surely a change.

We had a vehicle which has been SORN'd for a while, and received a renewal email in March which we replied to indicating the policy was no longer required, and should not be renewed.
It should be noted this came from the fairly 'normal' email address smallbusiness@directlineforbusiness.co.uk (not do-not-reply@ or something similar)
The email sent successfully, and no rejection was received (or bounce message indicating it was undeliverable)
Despite this communication, Direct Line renewed the policy and having complained (which, of course, we could only do by phoning them) about the lack of action on the cancellation they rejected the complaint on the basis that they never received the email and they include this;

Now, it's true that those words do technically appear in the email - but with far less prominence than even in the complaint respone - hidden away in the nonsense and small print with a font size 1/4 of the rest of the email and a contrast ratio of closer to 5:1 compared to 19:1 throughout the rest of the email.
It almost feels intentionally hidden.

However, the problem is much bigger (ignoring my shared, and commonly-held, views about no-reply emails!)
Companies should not be allowed to force you to use a different communication channel (especially a spoken one) to cancel a contract you entered into online.
This is a fundamental imbalance, one that causes consumer harm and is potentially incomaptible with the Equality Act as some people will be unable to use the telephone (for various reasons).
This will be with the Ombudsman shortly, so we'll see what they have to say I guess.