I think the answer to your cost might be in your question. Was your boyfriend a member of your household? If he was or was listed as an operator on your vehicle, that could be why the cost jumped. It is hard to say exactly without any information from the company.
If they take you to court over the money owed, it would make sense to serve them with discovery and obtain the policy breakdown as to cost. You can try sending them a letter asking for the information and see what they do.
You can always contact an attorney for a free consult ans see if you have a case they feel is worth taking, though Insurance companies are notoriously difficult to deal with and tightfisted.
These are generic informational answers, not to be construed as legal advice or creating an Attorney client relationship. If you have a legal issue, you should always consult an Attorney in your jurisdiction. You wouldn't ask a surgeon to talk you through a heart transplant via email, don't expect to do the same with a legal matter.