Tips to refuse the invitation politely:

Many time we receive an invitation that’s not exactly to the party of the year in your mind? We've all been there! We Don't have to feel obligated to attend an event just because you have been invited. The Invitation can be declined  while remaining in the host's good graces. Here’s how to politely decline an invite:

• Timely Response. Don't keep the guest waiting and wondering that you gonna attend the party ,a timely response would be great way to tell the guest in advance that you wont be able to attend
• Don't take the easy way out. Not responding to the invite and making up an excuse later on will not be well received.
• Thanking the host for the invite. Express how flattering it is to be included in the celebration.
• Schedule another time in the near future to catch up with the host in person if he/she is a close friend or relative.
•  Simple and short responses. Tell the host you are sorry you will not be able to make it this time, but hope they enjoy the party.
• Ask the host how did the event go. Everybody would like to talk about their great party.

  Anna Orlando, Krystle, AcidRain, Whoze and 1 other (2009).How to politely decline the request.            Retrieved from http://www.wikihow.com/Politely-Decline-an-Invitation