Cold this also be: "I then watched television"
Yes- it's one of the possible answers given
Could this be used in the sense of "I used to watch it, but don't any more?"
Possible, but not very likely. If I wanted to say that, I'd say something like "Ik keek toen nog televisie / Toen keek ik nog televisie".
Why "keek toen naar televisie" is wrong? Thank you.