Poor service from Accounts department!!

I am just not getting anywhere with MTN! They had a certain closing balance on my Dec statement, and a totally different opening balance on my Jan statement. I have tried to phone them, just to get cut off eventually, and I have sent a couple of emails as well. No one gets back to me, other than the sms's 2am and 4am today saying that I still owe them an amount. It is really ridiculous!