According to Vodacom i have short paid

Vodacom started phoning me yesterday. Didn't get time to phone them so I phoned them today. The lady that answered the phone said I short paid my account with a R150. According to the invoice I have paid the full amount that was requested as per their invoice. No they want to suspend my cell service of that. This unacceptable. Vodacom is going backwards. their service is very bad. they talk to people in a rude manner. When I asked to speak to a manager she told me straight I can help you with the problem.I have been a customer of Vodacom for many years. Lately I have so many problems with them it is not funny. They want to upgrade me anymore, reduced my loyalty points etc. I am tired of all this problems. Can someone please assist me regarding this matter.