Credit score down with 21 points

It's almost a month later and i still get calls from MBD (debt collectors) they keep increasing the amount that I'm supposedly owing. I tell them every day that cell c said it should be handled and i paid into Cell Cs account. My credit score is still down with 21 points. I'm still not happy i get called every single day it's as though nothing was communicated between them. I explain myself to new consultants everyday as if the previous one didn't make a note of what I said and I'm still regarded as a non paying client. This is a follow up review since im still not seeing progress