Debit order amount differs to schedule Business client

Joined Miway bus insurance 3 weeks ago, already took pro rata debit order and Jan premium although I asked for debit order date 1st. The debit order amount taken also differs to the schedule sent to me. Being a business account, I need an invoice for every debit, now amount differs. I emailed them on 25 Jan, no reply. Someone phoned me this morning but put the phone in my ear. I then phoned back and held forever, being told by first person I'm in wrong department. Held again, got through to Thabo ref ***, he told me pro rata amount was wrong and he would send me an invoice for amount debited. Still waiting...quick to take debit order but not too worried about letting customers know why the debit order is different to agreement. Quite disappointed as a new business client. Can someone please send me something in writing to prove why my debit order amount is different to schedule received. Needed by month end please for SARS