I would recommend speaking directly with your service providers in Brazil for further assistance. Most likely your NS-DXA2 doesn't function properly it was designed for use in the United States.
Thank you very much for your interest in our Digital TV Converter Box . This converter box is meant to be used on only with analog TVs that are not capable to convert a digital Over the Air signal when using an antenna. In your case, it is necessary to contact your cable company to find the best resolution.