Hi
How frustrating for you
I know someone who had same problem with UCAS after she left 2 GCSE off by mistake they wouldnt add hers either.
But, she rang the uni when she found out there was still spaces and explained the problem to them (even after being refused interview earlier) and they said they would review her application. To cut a long story short she got a place in the end for that year
So, give it a go-ring them and explain the problem and say youre willing to go up and show the certificate if necessary and see what they say!
Nothing to loose.
All the best if you try it!!
Ceci