Which department to get best deal on contract renewal?

Hi all.
New to this sub for please forgive of if I miss anything.

I can currently upgrade on my plus (switch up) plan.
But the upgrade quotes are a lot higher than the ‘new customer’ quotes:

I’ve been sent around the houses over the phone, but apparently there nothing anyone can do to ‘match’ the new customer deals.

Any advice appreciated:

For clarity:
Customer for 19 years (monthly)
Looking at iPhone 18pro (black 256)
Custom plan - classic 36 month, 30gb data:

New customer; £1 upfront £54 per month (20% airtime discount)
Me; 0 upfront £63 per month