"I got a very good seat" is past tense for the verb "to get". But if you say that, it could mean "an hour ago I got a good seat, and I'm glad, because I can see the movie very well"....and you are STILL sitting in that good seat. "I had a very good seat", is past tense for the verb "to have".

( i got a very good seat ) means you still have it ,but ( i had a very good seat ) means you was having it in the past but you don`t still have it right now .

I got a very good seat " it is in present" naturally with got but it'd be "get" I had a very good seat "the action is ended and it is past simple tense