It is obviously sinful for any one to physically hurt or insult other person over his or her choice in marriage. If your choice in marriage was not against Islamic rules, no one is allowed to object or insult you. Your parents want you to be safe and happy, and you need to understand the reasons behind their stand against your choice. You should never disrespect your parents nor reply them back. If you are sure that they are been misinformed about your choice, you should clarify the facts for them.
You need to always be very polite with your parents and keep on praying for them.
Wassalam.