Nissan Micra 1997?

Hi there,
The fan heater blower is nt working at all,it used to work on number 4....
I changed the resister, then it worked 4 two months then one day stopped,replaced the resister, worked for 2 week,,then stopped completely, put a new resister in,not working, changed fuse,still not working,fan itself worked fine,no sqeaky noise....
Heat does come through when I go over 30mph & goes on cold setting too...
Any ideas most welcome...
Thanks!!!