I can’t help you with your accent, but I can suggest you refocus your efforts.
I live in the UK. If I call a contact centre, I am often answered in India; for example, if I buy airline tickets.
I don’t care if the person I am talking to speaks English with an accent. The Western world is multi-cultural, and differing accents no longer raise eyebrows. But, I do care if the person I am talking to cannot speak good English – there is a big difference.
So, rather than focusing on attaining a mid-Atlantic accent, why not channel your efforts into effective communication?