Incorrect Data Billing

On the 2nd April my data balance was 2148mb. Between the 2nd to the 7th April i barely used data and now on the 7th April all my data is finished. I have looked at the detailed account that was sent to me and saw that data is being used in the early hours of the morning while i am asleep. I called the call centre to query and investgate. They said that the technical team will call me between 48 to 72 hours. This is not acceptable. i have had many contracts over the years with other service providers and never experienced anything of this sort. The call centre tells me that although there is no site open the internet is still in use. This is ****************. On the 7th April i spoke to the call centre and they confirmed that all my data has been finished, On the 8th i queried my data usage statement, i was told that at 00h19 am on the 8th April i used the internet. Firstly i was asleep, secondly, if i have no data available, how is it possible to use the internet. i have not topped up data. Do they know what is going on????<br> i cannot believe it will take them 48 to 72 hours to just call me, let alone investige. POOR SERVICE