Is it permissible to use a used ihram that is suspected of being stolen to perform Umrah?

There is no harm in you using the garment you purchased. What was mentioned to you about the possibility of it being stolen is from the whisperings (waswas) that should not be heeded. It is from the blameworthy, cold piety that jurists have warned against, and it is not among the doubtful matters whose avoidance is commendable. Scholars have stated that considering a remote possibility is not among doubtful matters, and they mentioned examples such as refraining from marriage for fear of incestuous relations, or refraining from using water in a desert for the mere possibility of it being impure. Al-Qurtubi said that piety in such cases is a satanic whispering due to the absence of any true doubt.