Lack of Transparency

I changed my account to a data only account with Cell C(5Gig + 15 Gigs Night surfer) in May of 2015.<br> Last night I finished my night surfer with the understanding it would switch over to my other data when it was done, only to discover this morning on balance check that that they now want R355+ for 3 Gigs + data that I used over, Meanwhile I had 4,5 Gigs left of my other data.<br> Call technical and they say the other data only kicks in at 6 AM, had anyone mentioned that I would have set the downloads up differently only to use the night data.