英文點寫? help!

Dear XXX,

Hello! This is xxx of (co. name).
Due to xxx leave his/her position as at ddmmyy, I had been pointed to
take over her/his job. I would like to take this opportunity to serving
you and your company in future. Any inquiry pleast don't hesitate to
contact me. Thanking for your kind supporting.

Yours Sincerely,
xxxx

I try my best
To dear XX:
This is XX. The previous officer already left, so I am the one who in charge now.

I am replacing the position of Jane Lee, who she had resigned last week.
or more official:
Please be informed that Ms Jane Lee had resigned last week, I (Mary Chan) am replacing her position effected immediately.

Dear Ms./Mr. XXXX,
My name is Carol and I have undertook the job of Sarah, who has resigned earlier......

2008-03-18 11:49:55 補充：
Correction: My name is Carol and I have undertaken the job of Sarah, who has resigned earlier......