@Georgealex an alternative to using the String Functions in Alteryx would be to use RegEx tool. Very powerful tool that can parse out specific strings based on patterns. The following regular expression should accomplish your goal. Although I will say it is a bit predicated on your prefixes. If it is just though 3 or only a handful this solution will work. If there are many more then I would suggest break down the issue into smaller chunks and branching out your logic through multiple parses. I think you would get a better result and easier to follow logic in the more complex cases. BUT assuming only the three prefixes then this will do just fine. I agree with @Treyson that Regex101.com is killer and key to helping you through using RegEx.
I've also attached a simple workflow. Hope it helps.