Data disappears despite following all advice

I took out an LTE wifi contract in December for 10 GB per month. Our data was finished within 12 days of first starting to use it. This made no sense as we only use it for email and normal browsing - no downloading movies/streaming. I contacted customer care several times, they finally advised me to change my passwords which I did. I also changed the settings on our devices to not update automatically. In January, however, the same thing happened. Our data was finished by the 12th despite us not even being at home for the first 5 days in Jan. I went to the Vodacom shop in Claremont and I requested itemised billing which I have still not received. I also took all our devices to the shop for them to check the settings - all automatic updates had been disabled. In February, the same thing happened. I went back to the shop and Leeroy admitted that the 4G network was unstable and data loss can happen as a result why wasn't I told this BEFORE I signed a two year contract? I cannot afford to buy hundreds of rands of extra data every month. We use the internet only minimally and the usage does not make sense at all. I want out of this contract as I am not getting what I'm paying for.