Rain not informing customers what the date change implications are

My network is good since i changed to 5G basic plan.but the service from rain is very terrible and feels like day light ******* cause i was supposed to make.payment on the 25th of November but i changed it to the 1st of dec with the mindset that if i put it on the 1st I changed my 25th payment.this happened a week before the 25th.but instead they i could not pay on the 1st coz now they said I was owing 1443.then I asked on facebook I called a no response until I started sending on the wall thats when they rep**** me.now how is it possible that they put date changes and not specify to the customer what that means?are we supposed to get.after I got a response they rep**** saying they can't cancel one date then i pay what's due to me...now I must pay 499 for October plus 499 for November yet I'm supposed to pay November in Dec...rain is post paid this is so frastrating for me as a customer coz i have a budget for October