3 way calling charges?

We just got our phone bill and it was doubled because of 3 way calling.My 9 year old uses the phone alot,but I'm positive she doesn't know how to do a three way call.Also the calls are all about a minute apart,plus the bill says has our phone number on it like we were at home and calling our own phone... show more We just got our phone bill and it was doubled because of 3 way calling.My 9 year old uses the phone alot,but I'm positive she doesn't know how to do a three way call.Also the calls are all about a minute apart,plus the bill says has our phone number on it like we were at home and calling our own phone number,doesn't make any sense,also we live an apartment and there have been a few times where I have picked up the phone to make a call and the lady that lives downstairs from us is on the phone and I can hear her.Could the charges possibly be coming from her phone?Lets say that the three way calls are coming from my daughters friend.Could we be charged for them?I'm confused.Does anyone know anything about this?We called the phone company but noone can help until monday?I figured someone on here would know.
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