Last year my aunt was denied boarding on an Air Canada flight to United States (US). My aunt is not a Canadian citizen, so she had to get a US visa (aka "port of entry" visa) to get into US. She applied and received her US visa with a "port of entry" period of 3 months issued by US embassy in Canada. Once she got to the airport, Air Canada denied her board the plane because Air Canada claimed the period of her visa is less than 6 month. The Air Canada staff could not distinguish the difference between a regular visa and a "port of entry" visa. Unfortunately, because my aunt could not speak English well, she could not explain the difference to them and missed her flight. Since she was in a hurry and she booked another ticket with Air Canada for the next day. Once she got to the counter again, this time the Air Canada staff apologized for their mistake in the previous day and let her board the plane with the same visa. However, the Air Canada staff did not offer her a refund for her missed ticket, and my aunt could not ask for a refund because she could not speak English well.

After a year (February 2018), with my help, she is following up with this problem to get a refund for her missed airline ticket by contacting Air Canada customer service through email. After filling out a ticket refund application on Air Canada's customer service website and providing all the necessary documents (Airline ticket invoice, related passport pages), Air Canada finally forwarded the case to the Refund Services after 3 months of follow up. It took the Refund Services more than a month to get back to her and decline her application by making the following claim:
"Please be advised that our records show that because you arrived at the counter 5 minutes prior to cut off, and there was questions concerning the validity of your visa, you would not have made it to the plane on time, so you were given a flight the next day for the additional collection and change fee."

That is absolute rubbish. My aunt arrived at the counter much earlier than 5 minutes prior to cut off, and since she had traveled with the same kind of visa to US in the past, she was confident she had all the necessary documents. So, there was no question or concern regarding the validity of her visa. Even if she had arrived 2 hours prior to cut off, she would still be denied boarding, because the only reason Air Canada staff would not let her board the plane was because Air Canada staff claimed the period of her visa (aka "port of entry" visa) was 3 months; and the Air Canada staff admitted their fault the next day. Then my aunt asked the Refund Services to provide her with a copy of their records showing that she arrived at the counter 5 minutes prior to cut off, because she did not agree with their records. However, in the last email, the Air Canada refund services wrote that they "aren’t able to assist any further with [her] request", and to "further review [her] claim [she] need to contact Customer Relations"; which takes my aunt back to the very first step of applying for ticket refund application again!

I was wondering if anybody could give an advice what should my aunt do next to receive a refund for her missed airline ticket from Air Canada?
Should my aunt apply for the refund application again? Should she take legal action against Air Canada? Is there another way to approach Air Canada?

Thanks in advance