Payment for forwarded calls that were not taken

In the last few month i did not use the flynumber although I continued paying the monthly charge.
The Flynumber wa forwarded to an Argentinian number (I was not in Argentina and did not take calls).
However, systematically and for a long time I was charged 0.13$ for forwarded calls.
Please explain and how to avoid this charge.
Best Regards,

Please forward the FlyNumber to VOIP/SIP and you wont have to worry about the per min charge

Or you can just forward to PBX and it wont charge ( You can leave it all unset in there)

My account > my flynumbers to change forwarding