New data used instead of older bundles

On the 31st July I purchased a winter warmer 1.2g allnet data bundle on *123# valid for 2 days for R23. I have 711mb left today. Today my monthly contract 1g data has been loaded. When I use data it is using the new data instead of the data I bought yesterday which has an earlier expiry date. I think this is totally unfair for me to buy a bundle and not get the chance to use it till the last day I boaught it for.