Is the lack of answered prayers, after saying mockingly and angrily: "My aunt and my mother's friends pray for me to get married, but I see no answer to their prayers," considered a reason for the prayers not being answered, and how does one repent?

Allah may delay the answer for a wisdom, or replace what the supplicant asked for with something better for him. Indeed, Ahmad narrated from Abu Sa'id Al-Khudri that the Prophet, peace and blessings be upon him, said: "There is no Muslim who supplicates with a supplication in which there is no sin or cutting off of kinship, except that Allah will give him one of three things: either his supplication will be granted hastened, or it will be stored for him in the Hereafter, or evil similar to what he supplicated for will be averted from him." Therefore, one should continue to supplicate and increase in it, and be keen on the means that make the supplication more likely to be answered.