I don't seem to be able to alpha sort this one
Because it's Alphanumeric, yes? So to simplify, CA303 comes after CA1234 when the latter is a larger number. If not, then please elaborate as requested, because sorting numbers in a text field will always produce undesired results. Your choices might be to split the alpha from the numeric (if they're not inter-mixed) or you'd need a sorting field of some kind.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.