1996 Other Fiat Models oil filter

We just recently changed the oil in our car and once we got home and revved it up the oil filter blew off so we figured it was the wrong size or he cross threaded it so we got auto shop to get us another one and they said that the one we had was still ok so we tried putting it on again and it was loose and didn't even have to twist it on so we called and had the auto shop order a new one and so they did and last night we put it on and it was pretty tight so he let it run and revved it a little last night and nothing happened. So we get up this morning to leave and he went to back out of the drive way and we heard a pop so we got out and the oil was coming out but this time the oil filter stayed on but leaked the oil out. What could be causing this problem?