Awesome buddy! Well done on your successful referrals.
Lycamobile UK (run’s on o2) has a referral scheme. Earn up to £20.
As already mentioned by wagstaffes lebara (runs on Vodafone) is an awesome referral scheme. Earn up to £50 per successful referral.
The ‘THREE’ network has a referral scheme. A pretty awesome one. Earn up to £80 per successful referral.
The SMARTY mobile network (runs on Three) has a referral scheme - Per successful referral you will receive a free month (and they currently have an offer to also get £15 account credit).
I have the next 16 years free of mobile service with them.
Voxi, Vodafone, BT, EE, offer Amazon gift cards.
Plenty of websites out there (such as Carphone Warehouse and Mobiles.co.uk) who offer incentives.