Not so sure it's a scam, not enough info to know for sure. Also not sure about what kind of classes. At first it sounds like online teaching, but then I get the impression there is also some in person teaching. This woman's English is clearly pretty poor, however that is quite common with Chinese English teachers, imagine that.

It might be that someone answered who doesn't speak English, cleaning crew or one of their staff. Believe it or not but not everyone who works in and English school actually speaks English. You might have called at a time of day when their simply was no English speaking staff in. It can be dangerous to jump to conclusions and make assumptions without enough information. I'd call back on another day instead of being so quick to judge.

I'll be the first to jump on any school or training center that presents itself with what I know to be sure signs of fraud, deceit, or any other kind of abuse of foreign teachers, however if no such signs present themselves I will reserve judgment. Give them a call back, and email her, set up a time to call so that she is there waiting for your call. If at that point the same thing happens, well that's different, she would be unprofessional for not being there for an appointed call, and you'd be best not pursuing it further.