All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
Undoubtedly, helping neighbours is something urged in Islamic Law especially if this is with the intention of calling a non-Muslim neighbour to Islam. However, this is not a sound reason for committing prohibitions.
Buying pork is forbidden, but since you did not know that those products contained pork, then we hope that you are not sinful.
However, it is not permissible for you to continue buying these products for them, and you should inform them that it is not permissible in Islam to buy pork in the same way you informed them about alcohol.
You should seize this opportunity to call them to Islam, and inform them about the recent surveys which show that pork causes serious diseases and that the Quran forbade it 14 centuries before these surveys were carried out. This will be the occasion to call them to Islam as the Prophet Yoosuf (Joseph) did with his two inmates when he interpreted the dream for them.
For more benefit on the wisdom of the prohibition of pork, please refer to Fataawa 81392 and 82887, and to Fataawa 86337 and 84349 about calling the Jews and Christians to Islam.
Allaah Knows best.