Shafted by the Transport Canada?

This morning I received a letter from Transport Canada informing me I
am being fined $250 for not filing a flight plan. I had flown from
Minot, ND to Regina, Canada on July 30, 2005. I had meticulously
planned the flight using the AOPA webpage on the subject (got all the
radio station permits, customs decal, etc.). I am absolutely sure that
I had filed and activated a VFR flight plan for that flight. I had a
squawk code and was getting flight following, but when I landed in
Canada the FSS couldn't find my flight plan to close it. I was
informed of the investigation by a phone call about a month after the
flight. Conveniently for Transport Canada, Minot ATC erases their
tapes after two weeks according to the manager of the Minot FSS. I
submitted a Freedom of Information Act (FOIA) request to the Great
Lakes Regional FSS as soon as I heard of the investigation in September
2005. As expected, Great Lakes said they don't keep records long
enough to fill my request. BTW, they were terrible to deal with. The
FOIA woman never answers her phone and never returned any of my calls.
The only response from Great Lakes FSS was a letter in February 2006
saying they no longer had records for that time period.

So, basically Canada says I didn't file a flight plan and I don't have
any way of proving that I did. Anybody have any ideas on how to
dispute this or had a similar experience? (AOPA Legal was no help.
Their only suggestion was the FOIA request.)

Thanks,
Bob