Unjustified increase of the size of my Dropbox

I have been using Dropbox since years, and I have a limit at 9.25GB (obtained thanks to promotions).

Until last week, my dropbox usage was at about 90%.

Today I connected via web and I got the message that I am at 213% !! (first at web login, then received a mail few minutes later)

I am sure that I did not upload 10GB to my Dropbox lately, and that I am still at ~90%.

But of course Dropbox gives no way to check this... even folder sizes are approximate...

So what happened? 

Now the sites tells me to upgrade and no way to talk with assistance - if confirmed, I will cancel the account and migrate elsewhere, as this is a completely unjustified move to force me to buy a higher forfait.

Any idea on how to solve? Someone at Dropbox listening?

Thanks,

Daniele