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Have you checked the stitch length? You can try setting it at the longest stitch possible and see if that helps.
Have you tried changing the tension?
Checked underneath to make sure there isn't something keeping it from moving?
I was waiting for you to answer my questions.
It should be set in the middle.
Attached is a copy of all the steps to go through in checking tension on both the thread and the bobbin. If one or other of these adjustments don't work, you may indeed want to think about replacing it, or taking it to a service center.