Thanks for reaching out. I’m sorry to hear about this issue with shipping rates.
To understand the situation better, it would be very helpful if you could share your store link and advise which product to add in order to replicate the situation with shipping rates. Also, what should be the correct rate showing up?
Once I can see the issue in real time and replicate it, that would improve chances of understanding the root cause of the problem.
By the way, if you already edited shipping rates then this rate in question (£5.50 Express Shipping (24 Tracked)) could be coming from an app. Do you have any shipping or fulfilment apps installed that could be overriding shipping settings in admin?