I know its silly to ask you for guidance how to improve my writing and communication skills in English. It's obvious that to improve one should read more, speak more and listen more.
I recognised that, however I don't seem to improve. I feel so frustrated and ashamed of myself when my written english is so bad. Recently, I received a very harsh criticism from my manager that my report writing skill is very bad. And my english is terrible. I'm bothered by the comment and I feel so bad! I don't know what should I do now to improve my writing skills. Furthermore, I feel so embarrassed when they knew I was top of the class during my graduate study and yet I can't write a proper report!
I really wanted to improve myself very much and at this point I'm quite lost as to what to do! I read and speak very often eventhough I'm not a native speaker. I need to use the language to communicate with my client. Still, I'm not showing any improvements!
Your English skills seem pretty advanced to me. Just remember when you are speaking in plural terms meaning more than one, you need to use s. For example you said your "English skill", should be skills and not is, but are. Also remember to try not to start a sentence with And.
Present and Past tense: you said "I really wanted to improve myself very much" should be I really want to improve....you are speaking in present tense.
I believe your level to be quite good considering english is not your native language.