More 3 GB of MTN data ran out in 3 to 4 hours.. Just like that

I bought a sim yesterday at checkers ( grey owl) and Rica was also done. So when I got home I purchased R39 data just to test if it's working as I needed the sim card for my router for work purpose . Then today this morning I purchased R149 data which is equivalent to 1.5 GB then in few hours it ran out.. And I did not video call or log into youtube. Only used that for emails and for systems that require internet but still it would not chow that much because all along I was using my cellphone as Hotspot and I am on vodacom and I would push work with less than 300mb for hours and it would not even run out...so after my data ran out I purchased another R149 (1.5 GB) and guess what its also get finished just like that. Tried to check if someone connected to my router but there was no one, I need answers .. Now I urge people to be careful with MTN services ... So now I am forced to change service provider because of this ******* called data from mtn