Employment & Redundancy Help?

I was made redundant in February and was given just 1 week notice. I had a job interview during this time which i had to travel a distance to so i took the day off (i also had holidays) when i got my last wage i was short paid for the day i took off. I have since found out that the company have hired another person even tho they told me they could not afford my wages. I received my P45 which was dated October when i left February and now they are telling people (my friends and friends of my family) that i was sacked. What can i do????