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 is His slave and Messenger.
If it is confirmed that the meat is not slaughtered according to Islamic rites, then it is prohibited to eat from it.
However, if the above fact is not confirmed but one just doubts about it, then in our view in Islamweb, it is not permissible for us to forbid for people what Allaah permitted for them; in this case one should say Bismi Allaah (in the name of Allaah) and eat.
For more benefit, please refer to Fatwa 81380.
Allaah Knows best.