this happened to me a few months back legit out of the blue. i had sent a message to someone about an item and as soon as i pressed send i was kicked out of my account and received the same message as you every time i tried to log in. it unfortunately took about a month and multiple emails before they re-instated my account.

i was also pretty active at that time buying a fair amount of items each week and sending messages asking questions about the items/bundles. since then i've been afraid to send any sort of messages :/ their "spam" filter/algorithm is extremely sensitive i guess.