1: the filling was deep and the nerve has been affected, i don't personally think this is the issue in your case as the pain in not prolonged in nature.

2: the white filling has been placed in one large instalment, this can cause shrinking of the filling when it is set and causing the tooth to become sensitive due to the pressure of the shrinkage on the tooth tissue.

3:the cavity was not sterilised properly and all the acid which is used to prepare the cavity before the filling has not been removed causing sensitivity into the tooth.

In my opinion the filling should be removed and replaced using the white filling material but the filling done under rubber dam, which is a device that causes the tooth to stay very dry, the cavity properly sterilised, the filling placed in small increments to prevent the shrinkage sensitivity. In my opinion this should solve the problem.

Hope this is helpful, if you require any thing else please do not hesitate to contact me.