You are a very lucky person. Here is how you should defend yourself.
Please be very honest to President Ma and Premier Chen and all people all media and upfront.
Good thing you did not get paid at second payment as I understand.
The first payment is during your congressman period. It is consider a election contribution during congressman(people's representative) period. It is totally legal in my opinion.
When it is illegal is during your President Ma's administration position. It is executive term. You cannot use your position to collect political contribution. This is where you are different from President Chen.
Therefore, you haven't violate the law because you did not receive the second payment. You are very lucky. So is Mr. Chen your plantiff. He did not brib you during the term where you cannot accept political contribution.