Dropbox keeps spamming me about my storage space running out

Dropbox keeps sending me emails and notifications about my storage space reaching its capacity, as if I've got 100 megabytes of it left or something. It says that if I won't buy another plan then I'm risking losing my files, and a dozen of variations of the same message.

 

I've been using Dropbox since 2010 and I've got a basic free plan of 2 gigs, but I've increased my storage space by inviting friends and doing "challenges", so now I have around 16 gigs of space and 13.5 of them are used. That is not "critically low on space" by any means, but I keep receiving so many spam notifications that it's starting to look threatening.

 

Either Dropbox has a bug in calculation how much space I have occupied by comparing it to the basic plan instead of actual space, or it's doing it on purpose to force me to pay. Also I cannot contact live support since I have a free plan.

 

I'm thankful to Dropbox for the service it provides but I'm pretty sure this is not how a service should treat its long-term customers. If this is a bug then I sincerely hope that it will be fixed as soon as possible.