Assured short hold tenancy to a company

An agent let my house out on an assured short hold tenancy to a company over 7 years ago. Since then I have been managing the house myself. I was under the belief that an assured short hold tenancy did not have to be renewed at the end of the 12 month term. I now find out that I cannot let to a company using an Assured short hold tenancy. what is the situation for getting this company to leave?