Data gone with NO EXPLANATION

I have 2 contracts with cell C with usage in excess of R1000 a month! On 1 of the contracts, i have 1Gb a month data, this contract is running for 23 months this February. on the 1/2/16, 1Gb came into operation as usual. With using just watsapp and watching a 1minute 40second Youtube video, I get a message saying i have 15MBs inclusive data remaining!!!!<br> <br> I call the call centre, and they say i need to check my settings as something is probably not set correctly, hence my data usage! In all of these 23 months i have never had a problem,or interfered with my settings, now all of a sudden, a setting is not correct?!<br> <br> My phone data usage shows 86Mb used since the 1st Feb, yet 900Mbs have just disappeared. The call centre mentions that i need to log a query that can only be actioned in 30DAYS??!! Really? Would cell C grants their customers a 30 day payment grace period?? With this kind of help to my problem, i have no confidence in renewing any of my contracts with you!<br> <br> I expect a full explanation as to what has happened to my data as this is unacceptable.