Reverb on blue tooth ear bud

Recently purchased an I phone 6. Also purchased a blue tooth ear bud/jam transit.

The ear bud works great with music. But when I call someone on the phone they get reverb ( or hear their own voice when talking).

I have tried to turn volume down, which helps, but then I cannot hear them.

The company send me a replacement thinking that it was the mic in the bud but it didn't fix things.

No trouble pairing or charging or with anything else.

How do I fix this? Have not seen any solutions on the web.

Is it me or the other parties I call?

Thanks!