Thanks for taking the time out to get in touch with us, it's much appreciated.
We wouldn't be able to send out direct MMS settings to the SIM card however, it does sound like you would need to alter the APN settings within the handset.
I would advise to delete any previous/current APN settings, input and save the following:
1. Tap the Menu button.
2. Tap Settings.
3. Tap Wireless and networks or More... (depending on your version of Android).
4. Tap Mobile Networks.
5. Tap Access point names.
6. Tap the Menu button.
7. Tap New APN.
8. Enter the following data into the onscreen form, without changing any other settings:
Name - EE Internet
APN - everywhere
Username - eesecure
MMSC - http://mms/
MMS Proxy - 184.108.40.206
MMS Port - 8080
Authentication type - PAP
APN type - If given a choice, select internet+mms, if the keyboard appears enter *
9. Tap the Menu button.
10. Tap Save.
11. Enable the newly-added APN by ensuring the line is ticked, or the radio button is lit bytapping on it.
12. Check the notification bar for 4G, H, 3G, E or G with up and down arrows beside it, which will indicate your connection is working.
I would also advise to delete any previous/current stored network profiles that differ from EE/Plusnet.