Dodgy radiator fixing. Plaster wall help?

I have rented a house and been here for 7 weeks. The only place the sofa can go is against the far wall and behind this wall is a double racked cast iron standard radiator. I know now and then i have puled the sofa away from the wall as it sometimes touches the radiator but today i was hoovering. I dropped the nozzle at the end and crawled behind my sofa to get it. My **** banged the radiator and the whole radiator came away from the wall. Luckily it never fell on me. I noticed that the radiator was attached with brackets onto the plaster wall with one 5cm plaster board screw in each corner. DRILLED DIRECTLY INTO THE WALL WITH NO SUPPORT. Am i right in thinking that this was an accident waiting to happen. Plaster board walls are only good for pictures etc, not a double racked 1.5m long radiator? I just want to get my facts right before i go to the agency to complain. It must have been loose from the previous tennants banging the sofa against the wall. No way in 7 weeks can this occur. HELP with advice please. Andy