Your Beko is plumbed into to a sink waste and I'm guessing you plumbed it in yourself!
Make sure that the waste hose runs upwards from the machine to a point higher than the sink trap (and let the hose fall downwards towards the sink trap spigot connector.
If you look at the run of the pipe, If you let water out the plughole of your sink, can it flow down into the washing machine? Connect it as above (ie the waste water from your sink cannot run uphill and down into the machine.
If you have the installation instructions for the machine, Reconnect the waste hose exactly as suggested in the picture diagrams most washing machine manufacturers supply in their instructions.
John Smith
August 2006