A level Philosophy results query URGENT

Hi
Can someone please check this,I think there is mistake in AQAs grading for my results.
Unit 1 raw marks 73/80, they gave me a grade B
Unit 2 raw marks 63/100, they gave me a grade C
And overall got a grade C.
I lookedat the raw marks grade boundaries and found I got an A for unit 1 and a B for unit 2. I converted my raw marks to UMS and I am well into the A bracket at 179/200. I think they used my raw marks in the UMS garde boundaries without converting them to UMS points. Both my raw marks and UMS points show I got an A in Unit 1 and a B in unit 2 when I put them in the correct grade boundaries. My exams officer says that it is extremely unlikely that AQA have made mistake.But I really don't see how getting 75% of the marks gives me a C.
If someone can check this as quick as possible because we have limited time, thank you very much.