Was this a mistake on my part ?

In 2013 I took a par time function at retirement age 66 and delayed my social security in order to receive a higher pay out by the age of 70
I just learned from my online account that I accomplished the opposite and my estimated pay has been reduced, compare to the year before.
Could you give me an explanation as this is not what I hoped to achieve with delaying my retirement?
Thanks in advance...