Exorbitant cellphone bill

My cellphone bill has soared exorbitantly over the last 8 months or more . My interactions with Altech Autopage have been futile. I upgraded to a Red Advantage package to enjoy the allocated 1gb and other benefits. I am extremely conservative with data usage. Last week I received a message stating I 've used all data, the only app I switch on periodically during the day is what's app. I upgraded sometime last week to another 1gb by phoning in. Thereafter over this weekend my red advantage package kicked in so I received another 1gb . I had 2gb by the weekend,yesterday Sat I get a message that I have no data left because I have used all my data bundle. I know for a fact I have not as I'm very conservative about data usage. Rarely use the Internet , manually switch off applications that could consume data. The only application that could use data that I use is whatsapp and that to I will switch on cellular data to receive and respond to messages and thereafter switch off data. Altech Autopage I need you to respond please and look into my query as this is costly and frustrating . Regards Nerina Naicker