hi, noob with question. can a landlord rent same property twice?

short story is this:

Moved into a property in November on 6month lease. Due to many problems, Damp, Mould, Dangerous bathroom and noise problems with neighbours. we decided to leave in early March, landlord refused to allow us and insisted we keep tenancy until end of may but lowered rent to £500 knowing full well we weren't living there.

Now today i notice he's put it back up for rent at the end of March, effectively this means for April and May he could be getting 2 lots of rent on 2 seperate leases. Is this legal?

hope you can help.