I sold my IPAD Mini on ebay I need to deactivate my icloud account and my apple id how do I do this?

I sold my broken damaged IPAD mini on eBay now that the buyer has the product he has somehow been able to power the device on without spending a fortune but what I need to know is how do I deactivate my iCloud account and apple id that is linked through that IPAD mini? I have a very unsatisfied customer wanting to give me bad reviews on eBay so I need to figure this out. I have all the log in information but no device which is with the buyer. Do I need the device in order to deactivate these services?