About 3 years ago we had renters in a house up north and they did not pay their electric bill to Consumers Energy. When we evicted them and then closed the electric account. At that time we asked Consumers Energy who was responsible for the unpaid bill and the company said the renters were completely responsible for the debt and they would follow up with the collection from the evicted family.
Here is a link to the Michigan's Attorney General's office contact phone numbers:
The employees there may be able to answer your questions about who is legally responsible for paying the unpaid bill and if the Consumer Protection Agency can help you file a claim against the company.
Most likely the company is going after you because in the past when dealing with a similar situation the wife just paid the bill and the company was able to collect the money without a lot of effort. Is it legal? I don't know. Being married to him while the account was active may make you responsible for the bill even though your name was not on the account.
Good luck and let us know how it turns out!