Brand new sewing machine....top thread jamming underneath.help please!?

I bought a bernina activa online so can't go instore for help. I've played around with tension, checked both threads a million times and the manual doesn't offer any help. I put black thread in the top and white in the bottom to see what the problem was, and every time I sew it jams after a few... show more I bought a bernina activa online so can't go instore for help. I've played around with tension, checked both threads a million times and the manual doesn't offer any help. I put black thread in the top and white in the bottom to see what the problem was, and every time I sew it jams after a few stitches but also any stiches it sews on any setting look ok on top but underneath, it is all a big tangle of huge amounts of the top thread. The bobbin thread is just lying in a straight line with all these loops of black top thread around it. This is my first sewing machine and I don't know what else to check. The manual is pretty useless as far as troubleshooting, it's about as much use as windows help. I know the machine settings should be ok because when the machine arrived it had the bobbin thread inside and there was a scrap of fabric with perfect stitching on it under the foot so it had been tested and works. I've tried turning the spool and bobbin to go in opposite direction but nothing has helped at all. If anyone can tell me what to do please I would really appreciate it! Oh and... no need to tell me to ask someone or get lessons. I just want a bit of help with this particular problem as I have just got my new sewing machine and can't even try it out yet.
Thanks
Update: If it is tension: I've tried changing the top thread tension. I think the bobbin feels like like it is dragging more than the top thread and there doesnt seem to be any tension at all in the top thread even putting it on a higher tension. the manual isn't hugely informative but im 99% sure i have it... show more If it is tension: I've tried changing the top thread tension. I think the bobbin feels like like it is dragging more than the top thread and there doesnt seem to be any tension at all in the top thread even putting it on a higher tension. the manual isn't hugely informative but im 99% sure i have it threaded properly. I have tried investigating to see if i missed anything in the threading but i dont know how else i could thread it!
Update 2: And it's the same thread top and bottom just different colours and i have tried 2 bobbins, one that came with the machine already wound and one i did myself on the machine and there doesnt seem to be a problem with them. i've turned the bobbin around and tried threading it the other way around, basically... show more And it's the same thread top and bottom just different colours and i have tried 2 bobbins, one that came with the machine already wound and one i did myself on the machine and there doesnt seem to be a problem with them. i've turned the bobbin around and tried threading it the other way around, basically fiddled around with it and nothing has made a slight bit of difference.
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