Mystery 3.5GB data usage at 01.40 in the morning!

I have been getting some mystery data usage while roaming in Norway. The first instance was for 3.5GB at 01.40 in the morning, the next day there was mystery data usage at 01.13 albeit only 10 MB. I'm a bit miffed that this has used the majority of my 5GB monthly usage in one go. I have no auto downloads setup on mobile data, so I am very concerned.
Is there anyway of getting Lebara to check this out?. It has never happened in the last 6 years I have been with Lebara.

Both Android and Apple have a setting where you can review your data use. Have you checked this yet Bigbruv?

Having done some more research I have determined that this is a quirk of Chromecast/iplayer. In that even when you have downloaded a program which you intend to cast to chromecast. The chromecast effectively still downloads the data twice from the original source rather than directly from the device holding the downloaded program. It should carry a health warning!
It would have been helpful if Lebara could have helped identify the source of the data use and proper timing. Lebara said data use was at 1am, when in fact the chromecast use was much earlier in the day. This caused much confusion.

OK good to hear that you managed to figure out the cause of the data use Bigbruv! I agree there should be some sort of warning if the data is going to be used twice.