Where to report coop griefing

[Molten_Savage]

I got a dm last night of a friend of mine saying he got into a coop member's account, and told me to "have fun" and to not be rude all cause i muted his dms since he was being petty and annoying. I get on after the reading that message to find heaps on obi placed as a massive cube on my island, whilst also incasing different minions of mine to make it even more of a pain to fix. Is there any way i can report this or

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