Free magazines sent to Brasil are exempt from any duty much like books. How do I make sure customs don't charge?

Hi

We send around 30-60 free magazines to Brasil every month fr the last 6 years.

if we send DHL we are always charged a customs charge, but no other shippers normally do this. This month we were charged a customs charge again of R$70 (around £25, although I have not seen the invoice yet so presumably some of this is from TNT as an admin charge) with a declared value of the magazines of £5 and a customs code of 49.02.9000 on our invoice, they are sent from a non vat registered company in the UK to a private individual in Sao Paulo and we declare the CPF number on the customs invoice.

The magazines are distributed free to a few foreign language schools and otherwise are for friends and family there.

The magazine is paid for by advertising (and subsidised by em as this doesn't always cover the cost) and is distributed free in 11 countries in Europe. it is a general interest magazine for Brasilians living in Europe.

Firstly, should I be paying any tax, have things changed? When I checked a while ago the value of the magazines was below the import duty rates for even ICMS or any other duties as it is a free magazine.

As basically the magazine is non profit making and is free how can I avoid the customs charge being added in future as I believe they are exempt.

Thank you

Kevin
Spittle