Hello Hossein!

There's a website which I'm sure you will love:

http://www.forvo.com/

It provides thousands and thousands of words pronounced by native speakers so you can hear different accents!

I hope it'll help :)

For most speakers, the "t" is silent, i.e. not pronounced. In some parts of the US, the word is prnounced as /ɔfn̩/, and in other parts as /ɑfn̩/.

http://en.wiktionary.org/wiki/often

You may find this link helpful:

http://www.grammarphobia.com/blog/2007/07/often.html