BAD SERVICE EXPERIENCED

I've been mistreated by vodacom and feel my consumer rights are violated. I took a contract last year and after noticing that i was not debited for 2 months i contacted vodacom and enquired. It was only then that they advised that i had a credit balance and that they will deduct from it and as soon as it was finished they will start debiting my account. The credit was finished in November and they did not debit me not even a phone call to advise. Now 3 weeks back i received a nasty statement stating that if i don't pay the outstanding amount within 7 days i will bw handed over to colections and this will ruin my credit score. How can you guys trat me like a common ******** when you were the ones who failed to do your job by not debiting me when you even had my account details. Now I'm being informed that i must make an arrangement yet no one from your side is willing to take accountability of this issue. I dont have a problem paying but what i hate is being rushed about the 7 days and that i must make arrangements and also that i am now threatened about my profile. What i require from you is a call of acknowledgement that they admit that they were at fault and how how they will make a payment plan suitable for me. Please contact me advise me of a way forward. Your angry customer Zandile