Imam Ahmad (rh) was asked about who to take ilm from when he’s gone and he said, so and so person, and they mentioned he doesn’t have many masaail, so he replied that indeed he is righteous and the righteous are guided to the truth.
Taken from jaami uloom of Imaam Ahmad (rh)
We can learn from this that just because someone has studied many books and memorised thousands of texts doesn’t mean everything, rather they must be righteous with honesty, trustworthiness and general good character.
This includes communication, and it includes fulfilling one’s promises.
Unless one forgets accidentally, if someone says they are going to do something and they don’t do it, it reflects very very badly on one and is from the characteristics of the hypocrites.
Similarly, if you know someone is trying to contact you, and it’s important, it’s vital there’s communication! The Prophet (saw) was never like this! He would reply and respond.