Subscribers Count Exceeded Your subscriber count (7701) has exceeded your plan limit of 10000 !!!

Subscribers Count Exceeded Your subscriber count (7701) has exceeded your plan limit of 10000 !!!

The message : 
"
Subscribers Count Exceeded
Your subscriber count (7701) has exceeded your plan limit of 10000 . Please upgrade to continue sending this campaign
"

Is a bug ?
My subscribers are under my plan limit (7701).
But the application tell to upgrade.

Can you explain to me ?

Thank's