From the symptoms you are getting there are two possibilities :
1. There is some paper or something jammed inside. Or the rollers have got misaligned due to previous jams. Or the paper jam sensor is malfunctioning.
2. The rollers have worned out with usage and need to be replaced. Its unlikely if its a new printer.
Try to do this too :
Open up the printer and blow air in it (using compressed air can) to remove all dust.
Try to rub the paper feed rollers with some rough moist cloth to increase its traction (grip).
If all this doesnt work than you need to send printer to Brother as your printer is in warranty and they will replace the rollers and the sensors.
Dont try to repair it yourself as it will void its warranty.
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