I want all my airtime refunded!

Telkom has been giving me problems ever since the lockdown. Whenever I try to make phone calls it tells me that I don't have sufficient funds or my airtime is lower than R5. I don't understand this and I'm very frustrated and I don't owe the company money. If I buy R12 airtime I have to buy more because it won't get through it will tell me that I don't have airtime. This is wasting my money because I have spent more money than I should have spent on airtime and data because of this!