Why would I want to write a letter? It's 2022 not 1922.
I thought Virgin Media was tech company!
Why no online chat facility?
Why no email address that gets answered?
And if you're planning a price rise you KNOW is going to be contentious, why not man up the phone lines, for example by signing up one of the many contract call centres who provide short term customer interaction? Or offer an on-line cancellation option so that customers who simply wish to cancel don't have to deal with VM's criminally poor telephone customer service? Or phase the price rise notifications over a longer period?
The "we're so busy" excuse doesn't wash when the only reason VM's contact centres are busy is the company's inability to do resource planning.