What to do?

I should have to send money to known account but the physical address Fruskogorskog odreda 71 does not exist in the phone book
and the data source,ex wife, exists on Fruskogorskog odreda 7,Petrovaradin ,21000 Novi Sad,Vojvodina ,Serbia
Answers:
Why don't you send the money directly to her bank account? Bank to Bank transactions offer more protection.

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The new address may not have existed when the phone book was printed. You don't give much information, but if you are attempting to pay child support to your ex wife who exists at that address, I would recommend paying through a third party -- perhaps deposit directly to her bank, or have a government official verify the address in some manner to ensure that the address does exist. If you can make your payment traceable (i.e. require a signature for receipt) that is best.