High internet tarriffs

I used round about 10Gig data, on my contract I receive 2Gig free per month, which I don't always use. the day after I received an e-mail, stating my internet usage was suspended due to high usage and that my bill is R5379.52, it is outrageous that they charge R2 per megabite, which makes it R2000.00 per Gigabite, and when I wanted to make arrangements they told me I must waight for next month for it to appear on my statement. I have 4 contracts with them. I cannot understand how they can charge this much if other outlets can charge R160.00 for a gigabite.