Depleted airtime

I have been having a problem with their network for a while now, especially when I am at home, which got me to stop buying monthly minutes be I struggle to finish them because poor network coverage, so today I bought an airtime with the intention of buying all in one bundle, so I bought for the exact amount, and I had data but I still switched off my mobile data so as not to waste it, but by the time I was making the purchase, I had insufficient fund to make a purchase, which is a reap off and this is not for the first time this is happening and they never seem ready to take responsibility, except to put a blame on you, now I need to use these services I was intending to buy, but I am forced to look at something I was not looking at buying at all because funds available......