Call 0800 956 6000 (option 2 and then option 1)
I got Y550 for £22.99 with no topup required or delivery costs. Apparently you need to have a EE sim and topup'd and they give loyalty discount every 6 months.
They also have Alcatel Pop S3 for £27.99 and Lumia 635 £34.99
Initially I was told Y550 is £34.99 + £20 topup. But, then checked my account and offered £27.99 after loyalty discount. Then had to bargain to get it to £22.99.