@Meekleton 
If you are looking for some insight I might have some for you. 
This might explain the possible why this happened to you but will not solve your problem.
Theoretical scenario start:
If you use an unknown/untrusted/unsecure platform to log in with your account and it has been sanctioned your account could then also be sanctioned. For example logging in to play at an internet café could end up having your account banned if said platform at the café has had a hardwire ban. internet cafe's are not safe for personal accounts as one does not know what others have done before you on that platform and you also do not really know what has been installed on that platform.
The same kinda goes for using other peoples platforms, do you really know what they have done or have installed on their platform.
Their is also the flip side of this for someone letting others use their platform for gaming what if that other person does something to violate the ToS and gets your platform banned.
It is always best to keep your account and platform safe by not letting others use your platform or account and by not using other platforms that are not your own.
Bottom line to keep your account safe is use your own platform, use your own account and do not let others use your platform or account, anything else is unsafe.