1 GB in 1 day and bad Reception???

On the 31 of May I went to MTN and bought a 1 GB - 1 GB free voucher for R160. I just as normal do whatsapp and the occational email etc, how on earth is it possible that my usage can be 1GB for one day, yesterday I had 2GB this should last for the entire month - a day later and I only have 1,07 Data left, how does MTN explain this? I dont watch videos or youtube how could I use so much data if I only send a few whatsapp messages? mTN need to reinburse me with data as its a huge mistake on their side, I normally buy R15 - 100mb budle and that easily last me a week or more so how does MTN explain 1 Gib in a day? Is this a ****? Also I live in Oude Westhof in Durbanville a very upmarket area but the reception is extreamly bad, so bad that I sometimes have NO SERVICE