It happened with me once
You probably just bought some mobile redirects
They send you more traffic than you pay for most of the time
Never extend
I extended once for over 15$ and got nothing ! 0 traffic. Opened a ticket and they told me the next day that they have sent more traffic initially so the money went to the previous traffic order.. It does suck balls actually IMO
Hope it works well for you and let me know if it is a mobile campaign that you extended