There very much is a 't' sound in 'often,' but it depends on how you talk (whether or not there was before, language changes). If you're saying native speakers are saying it wrong, then I don't know what to tell you.
Maybe you're young or speak a nonconventional dialect. In my local dialect (Midwest American), the "t" is almost never pronounced. I wouldn't say it's wrong to hammer the "t" home, but it sounds clumsy to my ears.
Linguists call it "spelling pronunciation": pronouncing as written, pedantically, despite not hearing it spoken that way. It's silly, but less silly than many other things. Of course, the more it happens, the more other people hear it that way and come to believe it is normal.