Why using **21*1+phonenumber# unconditional forwarding changes my iPhone call forwarding to that number?

I am traveling in Taiwan and I noticed the last two months using the "iPhone Call Forwarding" feature, I am still being charged for $0.25 each incoming call.  Last year when I was in Taiwan, I wasn't being charged at all . Is there a change in policy on this?

My second question is then:

I used the **21*1+phonenumber# unconditional call forwarding feature and "I noticed it actually went ahead and changed that to the iPhone Call forwarding to that phone number". This is no different than I change the iPhone call forwarding myself. If this is how it is, I believe I will be charged for $0.25 again each time someone call me from the state to my phone number and then my phone will actually call forward to the State voice mail and then of course I would be charged.

Can someone verify what I said is true? and if so, is there a better way to do unconditional call forwarding​ so I won’t be charged for any spam calls?

Thanks for any comments or suggestions?

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