Closing out a rented storage unit

We recently emptied out a storage unit where we had stored our son's apartment furnishings when he transferred out of state. We had rented it for just over four years. My name is the one on the rental agreement. There is a clause that says the unit must be closed out/closing paperwork signed on site, etc. We tried to sign out on Monday, Oct. 1, but watched the office person walk off down the street with someone. No one was in the office and the doors were unlocked. We had to leave. My husband returned alone on Wednesday to remove the final two items. He also tried to close the unit out. He was told he couldn't because he wasnt the one on the rental agreement. However, the document said my "agent" could also close out the rental agreement, but they did not accept him as my agent, eventhough the office person had chatted with us over the past several days, knew we were working together on moving things out, etc. Now the office manager is insistenting that I return, in person, to sign the documents and close out the agreement. Since we live in another town and a bridge under construction is involved, I asked that he send the documentation and we would have my signature certified and/or notarized. He refuses to do so, and insists that I have to appear and do it in person. He is totally inflexible about this, and is threatening to continue to charge rent on the empty unit and turn it over to a collection agency. We have put in writing our intention of no longer using the unit, our unsuccessful attempts to sign off on the unit, and our request that the paperwork be sent so we can have it completed and legally certified. He has declined and insists I have to return and sign the documents in person. He insists it is a legal requirement. What are my options?