I bought a car (Mobile phone) charger.?

I used it and it fused my car radio and the lighter itself and its not working, so I took it to a mechanic and thought they fixed the situation, but they didnt fix it as it fused on me again when I inserted the carcharger in the lighter slot.

Does anyone know, how I can fix this and what the problem could be.

Please only answer if you know what you are talking about.

Cheers