How can I get a renewal discount?

Hi all! My contract is coming up for renewal, but CF haven’t been able to offer a discount so far. I’m interested in the 2.5 Gbps Premium WiFi Full Fibre Broadband package. I’m currently on the 1 Gbps Fibre Broadband (Standard) plan, which I signed up to two years ago, prior to the introduction of CGNAT. Does anyone have any tips on how to successfully negotiate a good renewal discount?