Anybody know why DATA ROAMING gets greyed out? And how to bring it back?

[JulesOnVoda2017]

Running on S7 Edge and after a few months of travelling abroad without issue, last nigth I landed in the country of choice and found I had no cellular data.  Vodafone's SMS upon landing and turning on my phone told me I had roaming data, my mobile data notification informed me of the same thing, however delving into the SYSTEM I noticed that the Roaming Data option was greyed out and unselectable.

All ideas welcome as after 4 calls to Vodafone I feel they either don't care or could not tell their axxx from their elbox.

[Will]

Hi @JulesOnVoda2017

Could you let me know what Android phone you're using? The device, model and the version of Android you're running will help me get you an answer.

If you're able, please attempt a manual roam as your device may have set to 'Home Use' (The wording of this option differs depending on the manufacture) and will block any roaming.