Responsibility for Funeral Costs?

You say beneficiary - does that mean beneficiary from a will? Has the will been executed? Was there an executor? Generally, if a normal will is executed then funeral costs would be paid from the estate.
Did all of the people involved have an opportunity to participate in planning the funeral and agreeing to the costs? Was it discussed before the funeral as to who would be responsible for paying the debt? Who signed the contract with the funeral home? Have you discussed this problem with the funeral director as they are usually very certain as to where their money is coming from?

Lots of questions but you should think about the answers before making any legal decisions.
I believe the will and/or executor are the main person/things to review/consider first.
Here is a link to review to maybe help you understand how this is suppose to work (a will and responsibilities). There may also be state laws to consider if there continues to be a problem. I believe checking the contract with the funeral director would be a good first move.

blogs.findlaw.com/.../who-pays-funeral-costs-after-a-relatives...

Every state is different. Most times the funeral expenses come from the estate. I'm not sure if there was enough in the estate to cover.

If there is, it should not be your responsibility.