I gave up yesterday and called them back today, took them 55 minutes to connect me to a person.
Currently I pay £41.50 for 350mbps and phone, the loyalty discount was due to end in May and with the price increase due in March the price would have gone up to £65.75 in May. They have now given me the same deal, well pennies cheaper. £41 for same package for 18 months and won't have the price increase in March.
I normally don't accept the first offer and wait for retentions to call me back but took it this time as I thought I was happy with that discount last time so happy to keep it.
I did ask him if I could cancel the landline and he said the discount won't be as good and it would cost me more.