I worked for martins newsagents. I was working up to 76 hours plus per week and no overtime was given?

After a while with the company they had me sign the working time directive but not before they had me work some very long shifts. Also they put me in a store where I could not have a proper break while doing over 14 hours work and put into a store where I was on my own. They did not pay me until after a month when I left and this I was told due to an area manager not putting the correct date on my leaving form. Even though I have left for a couple of months now they still have not given me my final wage slip or p45. Is there anything I can do about any of this ? As I feel they owe me money as I did a lot of extra hours for them , they did not give a reason for not getting my wageslip etc.... I do believe the company is breaking the law all the time as staff are made to work extra hours which takes there pay under the minimum wage.