Can i sue my ISP

My ISP promised me a rebate of £5 each month. (It was agreed as per the terms and conditions). In the 1st year they failed to cough up - after a relentless number of calls and discussions with a umpteenth number of agents I got my rebate and was reimbursed a proportion of my call charges.

This was in November last year, however this year they are again remiss in their obligation. I can not afford to contact them every month to secure the rebate - they've assured me it would be automated, but it never is. I am tired and fed-up, it's extremely frustrating!!

.....breathe!

I have now decided to move to an alternative ISP, but I am keen to know can I sue them for the amount owed and the distress I have experienced.

Thanks,

Jay