I’m pretty sure this is a tech support scam: https://dfmo1jsc0ij7f.cloudfront.net/assests/eng_ff_auth.html?mid=9879&number=020-3695-9879&rb=JS8c127c78180b470db0afd4c526564666&browser=Firefox&os=Windows&geo=GB&site=14555701&p_num=
020%203966%204609
Their number is: 020 3966 4609