Airtime always goes missing

I have been expiriencing challenges with vodacom over the past few years, I load airtime , however whenever I try to make a call or use it, my airtime is depleted, I have contacted the customer countless times, however my airtime always goes missing. I am extremely disappointed with the service that Vodacom has been providing, I used to believe that Vodacom is one of the best leading telecoms company, however with the pain and headache that i have been subjected to, I am extremely disappointed and dissatisfied with them