Ekstra billing

I have uncapped wifi at home LTE from telkom. R599 per month. For the last few months my bill is almost R800. This is not what I singned up for. I signed up for R599 per month. Now there is event billing added. I do not need or want that. We are running on tight budgets in SA we cant afford ekstra that I didnt even agreed on. I agreed on R599 per month. Please correct this ASAP.