Seasonal work

anyone had any experience with JSA and seasonal work? 

i work at asda and my hours vary every month as im only on a seasonal contract ( 4 weeks at xmas, 3 weeks at easter and 3 weeks in the summer hols) they will ring me if theres spare shifts outside my contract so sometimes i may work 60 hours a month,sometimes i may work 4 or sometimes none. i never work more than 15 in a week as it means id have to sign off JSA. 

so when i sign on i fill in a form if ive worked to declare my work. however 3 weeks ago they stopped my JSA as it 'appears' to them i have a 'regular' job. i worked 19hrs in april, 17 hrs in may and 4 hrs in june!! at the minute im in a battle with JSA so not getting anything and feeling fed up i need to go through this when ive declared every hour ive worked! i do understand im only allowed to keep £20 a week but im just not getting anything!