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It is really, really difficult to achieve a nearly-native-speaker level of proficiency in another language and I understand perfectly well the problem you have described in your post. I've got the same type of remarks - only the language name was different in my case.
Two things may be helpful : first, ask native speakers around you to correct you - of course, most of them will tell you there is no need, as they understand you/your errors are sooo small it's not important etc. etc., but with time some may finally understand your need and correct you. Try to explain why it is so important for you and well.. cross your fingers to find some good souls!
The second hint concerns the accent and the pronounciation : try the technique called shadowing. It's very easy : listen to a speech made by a person with a really good pronouciation and vocabulary ( some high-level politicans or scientists may be of use here) and repeat aloud what they say (you can call it the parrot technique as well, I guess Emotion: wink The best would be to enregister yourself while speaking and then listen yourself - it is really unpleasant in general, most people don't like their voice, but it's really the best method to correct the pronounciation issues (and all kind of problems connected to the oral expression).
I hope this comment may be a little bit helpful!
Good luck!
Re: pronunciation.
When I was a kid, my parents made me listen to English audio tapes to help me improve my pronunciation. Not sure if it helped my pronunciation, but exposure did help my English in general.
Students: Are you brave enough to let our tutors analyse your pronunciation?