Can Service Providers price discrminate against existing customers

Background: Vodafone now do home fixed Broadband services as well as Mobile, If you are an existing Mobile customer they offer an extra 10% discount when you sign up to their fixed broadband/phone bundles.

As I was a BT customer, and BT exited the domestice phone/broadband market my fixed broadband/phone was switched automatically to Vodafone, nobody asked me if I had a Vodafone Mobile

After it happened I checked the deal I was on and discovered as I have a Vodafone Mobile I should be able to get an extra 10% discount.

After a lot of calls and e-mails to Vodafone, they are finally saying, sorry as you are now an existing (fixed) customer you cannot avail of the extra 10% discount offered to new customers.

My question, Is this type of price discrimination allowed?

FYI, someone moved this post from Consumer Rights, Not sure why a question about price discrimination would not be considered as valid for Consumer Rights?

I did originally consider posting it here also.........................

I had the same problem last week with car insurance - 5% online discount but when I , as an existing customer enter my details for a quote - no quote - contact the office. I spent 20 mins on the phone and no discount - take it or leave it - I left.