Airtime vanishing telkom

My airtime just keeps disappearing. In a space of 10 minutes I had recharged with R12 airtime and each time I was only able to talk for 2 minat most to a vodacom number until it cuts off and say my airtime is depleted. I recharged 4 times and spoke for roughly 9 minutes from R48 airtime. .....this is insane. Someone must explain this to me immediately, I demand an explanation because this is unacceptable