Hahah - so I'm a racist now? Heyrobot was whining that the school had 'not bothered' to learn her foreign surname - her words, not mine. I'd suggest that was offensive: If you want to be offended, how about the implication that it was the school 'not bothering', rather than a simple mistake?
In a school of 600+ (nearer 700) kids, there will always be one or two mistakes made. We had over 100 children with 100% attendance ( a massive achievement, BTW, and testament to the amazing teachers and support staff who work long hours and try really hard to get to know their pupils) - the certificates were handed to us for filling in by hand, at 1pm when the Assembly was at 2pm. Me, eating lunch with one hand, writing the certificates with the other, dealing phones/door/children with grazed knees, with the best will in the world will make a few mistakes. Yes it is the work of a moment to check spellings, but on 100+? When you do not have a moment? And honestly - at primary school, even secondary school (where I found that the name wasn't even filled in - we had to do it at home)- Achievement Awards are great, but usually chucked in their boxfile and thrown away when they left school. They don't count towards the degree, you know!
The OP states her child has an unusual spelling; when you insist on a strange spelling, you will find that instead of Dillon/Dillan/Dillen/Dylin/Dyllyn you occasionally get a Dylan. It's a mistake!
Unless it is on official documentation (Bank details, driving licence/passport, degree certificate) I'd suggest OP lets it go.
BTW I have an usual surname myself - easily mis-spelled phonetically, and sometimes hilariously. I don't get offended!