Supplication (Du'a) is one of the most powerful acts of worship. Allah listens to every sincere call.
And when My servants ask you concerning Me, indeed I am near...
Allah affirms His closeness to His servants and promises to respond to sincere supplication.
Three persons will not have their supplication rejected: the just ruler, the fasting person, and the oppressed.
Source: Sunan Ibn Majah
Allah hears every sincere supplication. Even if delayed, it is never ignored.