To request a MAC code you need to call your broadband providers. Please see the broadband providers contact telephone numbers here
You don’t have to be afraid to request MAC code as your broadband provider must supply you the MAC code within 5 days according to the UK law. Have your home phone number ready or your broadband customer reference as the customer service will want to confirm your identity. Requesting a MAC code does not mean that your contract will be terminated. In fact, you should terminate your contract after you have arranged a new contract with your new broadband provider. In this way you will not have any major downtime on your internet connection.
The majority of the UK broadband providers will send you the MAC code via the email in 24 hours. Once you have the code you can then switch to your new provider using the broadband comparison table