PLEASE HELP 😭 Anyone in payroll?? Or any teachers!

I am a teacher and was due the 5% increase this month and back pay to September. My payslip has been sent through and I’ve been paid less this month than last month WITH my back pay! All the “retroactive” payments are the back pay that was due from September. But they have taken a £875 deduction from my pay and I have no idea why (this doesn’t even add up to the amount of back pay I should have got!) 😭😭😭😭 I’ve rung my school and they’ve said they will try to speak to payroll but assume it’s correct. Please help me, I feel in my gut that this isn’t right and I’m being fobbed off. I should have been getting, £711 OMP, £788 SMP and £111 TLR (which you can even see on my payslip!!!), which comes to £1610 without any back pay. So how can I be getting LESS when there should have been over £800 backpay. Can anyone is Payroll make sense of this payslip?? I have been sobbing for hours, I’m struggling to make ends meet at the moment and now this! They’ve also had the audacity to email and say they over paid me by £212 in September so will be deducting that from me next month 😭