I recently had the same problem with my X8 and in the past their older phones have a similar problem with the charging ports. All they do is put the blame on you for the fault and say the warranty is void. Its useless arguing with them because they do nothing. They just say the same thing again and again that its "beyond ecnomic repair" they make the USB ports fragile so they break overtime with use. Best thing is to get it fixed by phone shop or buy an external charger.
Thats where sony ericsson make their money from by ripping us off. If you've made a complaints page let me know i want to join.