So now I'm confused...
Earlier you said "I got a replacement off ebay and went to get it programmed but its come back as faulty showing a code for brake pressure switch as well as vin mismatch. "
This to me reads that you installed the one from E-bay and it(the E-bay one) had a faulty brake pressure switch and a wrong VIN.
Not that there was a faulty brake pressure switch error before you did the swap.
C121D, or C121E
Unless you only swapped the computer side of things and used your old pump...
Then that would make sense.