buildings insurance confusion

jodenice

I moved into my flat last April. I paid the old owner for the pro rata cost of the insurance and was told that it had been transferred into my name. (I think though that she didn't transfer it, she cancelled it and got some money back - my mistake, should have checked)
The flat we live in is the bottom half of the house. We each a partial share of the freehold but not like the usual one, whereby you use a management company. We actually had to register with the land registry or something (equally complicated).
I am sure that it says in my contract that I am supposed to insure my flat separately. The old insurance policy that I can see that the other lady used says our address on it only. But phoning to get a quote from that insurance company she says both upstairs and downstairs need to insure with the same company (in case of a fire on the top floor etc). The top floor is rented and I don't even know how to contact the owners.
Our buildings insurance has run out and I'm not covered and I don't know what to do.
I hope I'm in the right place but will also post in the house bit too.
Help!