My washing machine model samsung 7kg front loader won't fully spin. when washing it won't always go around and on the spin cycle it is stationary but makes a noise like whizzing when it goes around.

Hi from retired Englishman in SW France- Frid morning 11:52.

It does literally sound as if the belt is slipping! This can happen with time. I would advise purchasing a replacement belt to be fitted by a confident/competent person- as you might well be!

REMOVE POWER.
REMOVE THE BACK.

The motor and belt should be easily visible- on most front loaders they 'stare you in the face'.
The motor's support bolts will require slackening, the old belt will probably come off very easily. The new belt is likely to be quite awkward/difficult to put on as it is a tight fit. Once on the belt requires to be re-tensioned by pulling the motor FIRMLY so that the belt is quite tight- if it is not already, that is.
ON NO ACCOUNT SHOULD A LEVER OF ANY SORT BE USED. THE ACTION COULD DAMAGE THE BELT, MOTOR AND BEARINGS.

I believe this should cure your problem.

Good luck,

John C