I bought a magnetic stirrer hotplate, it seems to heat ok but the stirrer does not work.

[sp33dhump]

the motor for the magnetic stirrer does not start up at all, even though the digital display says it is operating.  I contacted the vendor who has responded a number of times, and they ended up asking for a video of it not working, which i emailed to them. the last message i recieved from them advised me to fix it by tightening a screw. i advised 3 times in various messages that i had done this as it was in the troubleshooting section of the manual. this is not the problem as the motor doesnt run at all.. display says it is in operation. now it has been a few days and no further response had been sent from them. what should be my next action? make a claim through ebay or paypal? which is more effective? what are the differences in the actions taken by them?

cheers for any advice