Unreasonable expiry date of promotional data and false advertising

I upgraded my MTN contract on 7/07/2017.

The kind call center agent that assisted with the upgrade told me that as part of the promotion I would receive 10gb per month for 3 months.

My contract provisioning occurs on the 11th of each month. On 7/07/2017 I received the first 10gb valid for 30 days. Apparently, four days later on 11/07/2017 I received the second 10gb valid also for 30 days. I did not notice this as I was still using the first 10gb. On 11/08/2017 I received the third 10gb valid for 30 days. Thus I was given 30gb over a period of 2 months and 4 days and not over 3 months as I was told by the upgrade agent. Where I would have had approximately 90 days to use 30gb, I only had approximately 64 days.

When questioning a call center supervisor about this, I was told that if I didn't understand the terms of the promotion I should have asked. What I understood at the time of the upgrade was that I would receive 10 gb valid for 30 days each month for 3 months, was this not as per the words of the upgrade agent? Should I have asked for loopholes in the promotion or to ask how I could try to take advantage or cheat?

As a loyal MTN customer with a contract spanning for about 15 years, I expected more compassion from the call center supervisor, not a rude response. Why could the promotion not just have been implemented in a fair and reasonable manner? Why did I not receive the promotion in the way that it was advertised?