Same thing happened to me!
Yesterday when I opened DC, a pop up informed me that there was "suspicious activity detected" & that I would be banned if I did something wrong again. I didn't know what they were talking about & so I ignored the message thinking it was a mistake.
Today I WAS banned, when all I did yesterday was collect gold/food/maze coins plus a couple of arena/league/quest fights.
To give you an idea of my "suspicious activities": I have been playing DC for almost three years & I have two 3-star dragons (L43 Boulder & L41 Kitsune), 77 gems, 3.7B gold & 54M food. That's what the system considers "suspicious activities". Meanwhile I have been fighting 5-star L70 mythical dragons in the arenas since the 1st day of the empowerment thing started & nobody's doing anything!!!...
I contacted SP & I'm waiting for their explanation, but I seriously doubt there will be any logical & serious reply. I'm out of my alliance, arena, leagues, etc.
I'll let you know if/when I hear from them!