For the last 4 years, someone (unknown) has been signing me up for magazines. In all, over 50. How can I stop this?

The person who has been doing this is completely unknown. We have attempted to get copies of the subscription request form, but have only been able to do so from 2 magazine companies. It appears to be the same writing, but it is not recognizable to me. They also order gift subscriptions to other people in my name. I have even been sent to collections for this. I get probably 5-8 invoices a month from different magazines. How do I pursue this issue? How can I get this to stop? How do I find out who is doing this?