Overcharge on advance airtime

When you take advance for R10, 00, you get the message says they'll deduct extra R1. 10 and when you check, they took extra R8,90 in other words they charge R10 for R10 advance this has been happening for long, I was blaming my kids thinking they used my advance until I start to take pictures as proof of that, the service is very poor since they use Tobi, they'll never return your call, we need to speak to consultants.