Usage of new data rather than old data

I bought a MyGig 10 on 25 November, which is due to expire on 24 December, of which I still have 1.3GB left. I upgraded earlier in the week and received 10GB complimentary as part of the upgrade, but now I noted that my 10GB data, which only expires on 1 Jan is deminishing instead of the 1.3GB which I still have left from the MyGig 10 as purchased on 25 November.

So therefore I have now used a lot of data thinking that I am using up my MyGig 10, but then realised that I am actually using up my data which expires on 1 January, and after tomorrow 24 December, I will only have that left, as the 1.3GB will expire. Are your bundles not supposed to work on a FIFO basis? Now I am going to lose R78 worth of data just because I upgraded before the bundle has been depleted?