Hi, thanks for the info.
I ended up calling 3 customer services and they gave me something similar. There's just a few differences though.
For MMS proxy they told me 188.8.131.52 wheras the list you linked says it says the MMS proxy is mms.three.co.uk
Also for APN type, 3 services said default, the list says default + MMS, but my phone doesn't have the option so I set internet + MMS.
Maybe due to the debrand?