Can employer recover increased basic salary after early resignation?

I joined the organization “Adyogi” in January, where the employment contract stated that if I left the organization before completing one year, I would be required to pay an amount equivalent to two months’ basic salary, which was ₹33,333 at the time. This month, they increased my basic salary to ₹41,667, and I resigned in the same month. They are now saying that I must pay two months’ basic salary based on the increased amount. However, no such clarification was mentioned in the offer letter. They only stated that this amount was towards training, since they were investing time in training us, and that if we left before completing one year, we would have to pay. I am not refusing to make the payment, but I do not understand why I should be required to pay based on the increased basic salary when no exact or specific provision regarding this was mentioned in the offer letter.