Call work fine but why my cellphone bill doubled

So this app works ok for call but why the THIS morning Ill go and check my AT&T phone bill and my bill is that extra $50 from making calls on this app so the customer service representative lets me know that my bill is high for international calling because I use this app so you guys make it seem like you pay your money to make a call through you guys but Im getting charge for the connecting it to youthats absolutely absurd I am deleting this app

Kb154 about WePhone - free phone calls & international calling, v27.0.8