Can't solve my problem with data

I've got a new LG G5 and my data on this phone is depleting as fast as lightning.All my apps are set to update only on wifi and not on mobile data.I went to a vodacom shop and I have phoned customer care and nobody can help me to resolve this problem.I did a test on my phone and on anothet device I bought the same amount of data and went on the same sites.The data on my phone depleted 10 times faster than my other device.To give you an example I would buy 40mb be on the phone not even 5 min then I will get a warning sms you have 20 mb left after 30 sec another sms you 8 mb left and then my data's fini***** is unexeptable that nobody at vodacom can help with this problem, seeing that I'm a vodacom client.