Iphone6 screen broken - what is the cost of repair

$109 in the US. Prices will vary by country.

https://www.apple.com/support/iphone/repair/screen-damage/

iPhone Screen Damage Repair - Apple Support

Did you manage to fix it?

and in other countries besides USA

I am from Brazil and was told it is not possible to replace the screen and I was offered a "new"one ,for more than the double of the price of the screen.

My i phone is working perfectly but that and I just bougth it last August!I tried to get in contact with APPLE in Califirnia and it quite impossible

Whomever told you that is mistaken. Here is the information for Brazil:

Apple - Suporte - Central de Respostas sobre Serviços

The price for an iPhone 6 screen replacement in Brazil is R499 which at current exchange rates equals about $125. Not much different from the price in the US price.