share wifi connection

When I sharing my wifi connection with the macbookAir all the other devices are able to see and connect in it but no one is able to surf in internet.

The macbookAir surf in internet without problems. It is on line with a usb stick from the brand "huawei".

This problem appen from 3 weeks ago but before was fine.

I didn't change anything.

Do you have some ideas how I can fix this problem?

Tks