refuse to refund or replace faulty heater

We purchased a fan heater on the 05-06-2015. After a week's use,the front cover of the heater burnt through since then the heater no longer heats up. Took it back today for a replacement or refund. At first the floor manager excepted & replaced the heater then as we were about to leave the Branch manager refused & took the new heater away & had a very bad attitude towards us