The basis for most offers is to get new customers not to give a discount to existing customers.
Having said that I subscribe to the Entertainment pass only (I dip in and out of Sport depending on what cricket is being shown) and have had many offers to take up other passes. Last week it was three months cinema at half price, earlier in the year I was offered the Kids pass free of charge for a couple of months. I didn’t accept either.
Your best bet may be to sign up and then cancel, that often generate a offer from them, either whilst cancelling or a couple of weeks later.