And the unlimited data would have helped you. 3 do 15Gb for £25 a month on a contract.
The One Plan SIM-Only deal dropped to £15 from July, on a 12 month contract, or £18 on rolling monthly contract. I know OP isn't after another phone but if using the internet from one location, it would be possible to switch a cheapish Android into a hot-spot for 3-4 devices, as the One Plan not only provide unlimited data but tethering too. I've bought s/h Android mobile for around £40 on Ebay, but acknowledge not ideal for OP. I think Three should offer something higher than 15 GB given the way they have dropped the cost of the One Plan and that has texts and voice calls too...
I used Three from 2008 for 4 years (15 GB/month for £7.50 as there was a half price deal on in 2008) but that was on a dongle. Bought the ZTE mains-powered wireless router that shared the USB modem but unfortunately the One Plan SIM needs to go in a phone...
I switched to T-Mobile in January but after 6 months on their Full Monty (unlimited everything) they had removed so many masts here near Liverpool that they allowed me to cancel the contract 6 month early. (Handy I got £101 cashback when I signed up, so it ended up breaking even... ie pretty much free to me). I'm back with Three and £13/month gets me unlimited data and a low end Blackberry mobile (but the SIM is now in one of my Android mobiles).