What are the reasons for the non-response to continuous supplication for many years, despite adherence to acts of worship and supplication at recommended times and places? And does the statement "My Lord never answers me" diminish the reward of patience?

The answer to supplication is not limited to the fulfillment of what is requested. Rather, it may be by averting evil, or by storing up reward for the Day of Judgment. A servant's supplication is answered as long as he does not hasten. Be confident that Allah's planning and choice for you are better than your own planning for yourself. And good may lie in what has been withheld from you, in accordance with His, the Almighty's, saying: "And it may be that you dislike a thing which is good for you and that you like a thing which is bad for you. Allah knows but you do not know." So, continue to supplicate and trust in Allah's wisdom and knowledge, and be content with what He decrees for you.