Sorry to hear the replacement SIM didn't help IoM - I found this relating to roaming settings for the IoM, it's quite old info so may not be as relevant but may be worth a try in the meantime:
For Android:
Select Apps from the Home Screen
Select Virgin SIM Toolkit Icon
Select Roaming
Select Select Mode
Select Manual
Select International-you are done, go back to Home Screen
To Switch back when in the UK:
Select Apps from Home screen
Select Virgin SIM Toolkit Icon
Select Roaming
Select Select Mode
Select Automatic and go back to Home Screen
For iOS:
Select Settings from the Home Screen
Select Phone Icon
Select SIM Applications
Select Roaming
Select Select mode
Select Manual
Select International and you are done, go back Home screen to retry
To change back when returning to the UK:
Select Settings from the Home Screen
Select Phone Icon
Select SIM Applications
Select Roaming
Select Select mode
Select Automatic mode - you are done, go back to Home screen
**It is critical that you set the SIM roaming applet back to Automatic mode once in the UK or you will not be able to access service when you return.**
...please let us know if that makes any difference. Failing that, as Ben advised above hopefully this iwll be resolved once you have returned to the UK.
Tom