From what I can gather.
They may only take 15% of your credits. It seems you only had 1 credit. That's 100% of your credits. That is also me being really anal in this.
We don't know where it was conducted. If it was anywhere but a dingy back alley then they'd have been seen by cameras ICly and realistically set up on by Civil Protection who were not online to keep you safe.
We aren't wholly sure what "everything" is that was taken. For the clothing you lost your shirts, pants, and vest, if you had any, should have been safe as they'd not have fit the mugger. Your hat, coat, etc. were not safe however.
Are we sure these actions are befitting of the mugger's character? Was it something they would realistically do out of the blue like this? As the final bullet point of the rules states, and it's looking a lot like this was to get scripts and nothing more, it can be voided and refunded because they were, technically speaking, being a massive asshole.
Most importantly, in my opinion, it's very clear they did not wait even 2 minutes, never mind the required 10-15 post-mugging. This means they couldn't have even been caught were there units to respond, and they completely circumvented even this last barrier.
Also, dick move to go ahead and remove you from their SF list after the fact.
I may have missed something or got something wrong, here's the rules for muggings if anyone reading this has yet to read them.
http://taconbanana.com/index.php/topic/23081-guidelines-for-muggings/