New style ESA

Hi I want to claim the new style esa but having confusion with my employer (I’m on SSP at the moment) about the last day I’ll get SSP. The first week it was paid from was start Monday 4th December. But I get paid in a way where I get paid each month for what my contract is ie 40 hours a week and then the following month this gets adjusted up or down to what I actually did. So I didn’t receive SSP till end January pay for example for Decembers SSP. I’ve worked out that the last date I’ll get SSP is Friday 14th June. But I won’t actually receive it till end July pay date. What date do I put in the claim? The hr/ payroll are giving me an august date which doesn’t make sense and they won’t commit to a particular date etc. So what date do I put it ends on my claim? Please help.