Your Apple ID has been disabled

I have a set of iPads for use in school. 5 of them have recently started to display the message: 'Your Apple ID has been disabled'. I have contacted the Apple seller and we have gone through all possible solutions (resetting ID, logging in to ID on other devices, etc.) but it has made no difference. We have even deleted and reattached the iPads to the MDM.

I cannot update or download any new apps - even ones that are in the cloud ready to be downloaded, without getting the same error message.

Any help gratefully received.