This is coming from someone who has worked for Singer, Sears and a quilt shop & owns a Kenmore (33 years old), a Viking ( 10 years old) and a Brother (15 years old)
Whatever brand you have, call either the manufacturer which you can look up on internet or a local shop that sells that brand. Each machine has its preferences to what threads it likes and will work the right way in the machine. I have learned this over many years. Also make double sure that you are threading it the right way. Miss one area that should be used and it will cause this.
Also, on the Brother and the Kenmore, I have to hold the threads in the back for the first couple of stitches to keep it from jamming. It is just an idiosyncracy (sp) of those brands.
Don't give up on any machine---if one repair place cannot make it work, try another. Sometimes the first person may not have ever worked with that brand before but will not tell you that.