(although I think this is obsolete now, the output:
Code
$ apt-cache policy certbot
certbot:
Installed: (none)
Candidate: 0.10.2-1~bpo8+1
Package pin: 0.10.2-1~bpo8+1
Version table:
0.10.2-1~bpo8+1 500
100 http://httpredir.debian.org/debian/ jessie-backports/main amd64 Packages
You must not have the backports repo enabled. What is the output of: grep backports /etc/apt/sources.list.d/*