Reaching the storage cap, what does it mean?

I have a free account and 6 months ago decided to turn on the automatic upload option for pictures on my phone. Once they upload, I transfer them to a folder on my main computer where I organize all my photos. This has worked great, until a week ago. For the five or six months previously, it was just uploading my recent pictures. For some reason, now my phone seems to be trying to upload all the pictures on my phone, including ones from years ago. I do have a lot of old pictures on my phone. It didn’t seem like too much of a problem initially- I just would delete those pictures that it was uploading as my storage space got full. I’ve already downloaded those from my phone in a different way, so I don’t need them to upload. But after a while my Dropbox account would say that it was still 100% full and wouldn’t upload anymore, even though I had deleted all the pictures off. I even tried deleting other old files I no longer needed that had been stored in my Dropbox account. I thought that was weird, and decided to just leave my drop box account along for a little while and see if it resolved itself.

The problem I am facing now is that I just received an email with this information: Your Dropbox is close to reaching its storage cap. Once exceeded, you can’t add new items or sync changes across your devices.

I have tried to search what the cap is and whether my account is just dead when I reach that point. I can’t find any info out there. Anyone know what it all means?