Irreplacement of adaptor being in warranty period also.

My adaptor stopped working regularly from the day i brought this. After 3-4 replacements they started blaming me politely that how are you using this and how it is happening with you? But they used to replace it. This time when it stopped working(8th time) amd when i went to service centre they told me to bring my tab first. I complained with the sony care people. Then i went with the tab and they checked it too. After coming from there i mailed the main branch of sony care. Then they called me and say to bring tab again. I got angry and told that i am a student and i am not going again as they have already checked my tab. Today they called me again and told me that your adaptor got burned due to external voltage so this won't be taken in warranty period? Do i should take some action on it? Or i should be quiet?