How can I stop my dryer from spinning?

It tumbles for a period of time to keep the wrinkles out of the clothes. Just ignore it.

Unless you're an engineer call the service tech

Just about everything today is computerized. That means that the one operating your dryer is probably faulty. 

The timer switch has gone bad and needs to be replaced.  For the cost of the timer it might be cheaper just to buy a new dryer.  Otherwise leave the door open until you use it IF IT STILL HEATS UP, THEN IT IS A MINOR PROBLEM.  BUT COSTLY if you want an appliance repair guy to come in and fix it.  Really not worth it.

Your dryer switching panel is most likely bad.  I would first check the insides.  There are many YouTube videos that can show you how to open your dryer and get a look at the insides. (Unplug it first!)  You want to look for water damage or even lint where it should not be. If there is, clean it out carefully.   If nothing, then you know the panel is bad.  Sometimes they can be replaced DIY, but to be honest, it's prob best to get someone out to look at it who is a professional. 

When you close the door a switch engages to tell the dryer to spin.

There is probably a short in the switch and it needs replacing. If you are handy with a screwdriver you can do the job yourself in about 10 minutes.

Do a part search for your model to find the PART NUMBER you need to order.

You can also look for YouTube videos to see how it's done. I've fixed my washer and dryer several times and they're still running. But I'm mechanically inclined.

it needs a service call from a technician

Unplug it and call a repair person.

You unplug it and it keeps spinning? If this is true then you are just a troll because that is not possible. No power and it cannot keep running.