I think "There are twelve channels on my television" is more grammatically correct than "On my television there are twelve channels", yet the first sentence was marked wrong... reported...
Why would "my television has twelve channels" be considered incorrect?
Because you leave out "υπάρχουν" which means "there"
So what? It really has the same meaning as the "has" of English in this sentence. You should be happy for the opportunity to show that "υπάρχουν" can have the meaning.
It should be " τηλεόρασή μου", 2 accents.