Well done for your efforts. I hope you are not demoralised. I have a Swiss friend who came to London in his teens and he is the only non-native speaker I know who sounds like he was born here. His native tongue is German and so the linguistic differences are not too wide. It's often possible to detect that someone who was born and raised in England grew up speaking a different language at home, especially if their mother tongue is not European. There is a different resonance, even though they still have a British accent. I am saying this to help you be realistic that you probably will never sound like a native British person, even if your accent is quite close. And that's OK. Just for your interest, I heard a story once from WW2 of a German officer who parachuted into England wearing a British army uniform. He had trained in Germany to speak perfect English for the war effort and his time came to put it into practice behind enemy lines. When he landed in England, he asked a random local for directions to Bedford. He (quite reasonably) pronounced it /bedfɔːd/ instead of /bedfəd/ and he was immediately exposed as a German spy! The best laid plans...

Use a platform like italki to have conversations with people who speak your target accent, Watch TV shows and movies in your target accent and repeat everything they say in the same tone and emotion they do, as you walk around your house talk to yourself and narrate your daily life in your target accent.