Brother st371hd sewing issues

I need help. I've had this machine for a little over a year. I ran out of the needles they gave me so I'm using schmetz brand jeans needle. Brand new. I have tried multiple different settings. I only need the straight stitch and I can't figure out why the top thread shreds and the now the bottom thread bunches. I think it's a tension issue but I don't know what to do or what's best.

Main materials I'm sewing: faux fur, minky, lightweight scuba spandex