Issues surrounding my son's name

Hi,

I am new to the forum and looking for advice with managing my son's behaviour, particularly around the use of his given name and a name he has chosen for himself.

My son is 8 y/o and diagnosed with ASD. We have a EHCP in place and he goes to a specialist autism unit within a public school. As a family we generally cope quite well (we have a second son, also diagnosed ASD) but can struggle with change (going back to school today has been difficult for the past week or so). However, I am specifically looking for advice or ideas on how to deal with my son's name. Some time last year he asked us to start calling him Kebi instead of his given name, Alex. This seemed harmless enough as he had requested other names previously but it only ever lasted a short time. This has stuck ever since and we now routinely call him Kebi and he gets extremely upset if anyone calls him Alex. 

With hindsight we probably should not have gone along with it, but as I said it seemed harmless enough. We now have real issues with this. If anyone calls him by his given name, at school or clubs or anywhere, he has a huge meltdown and can attack whoever called him Alex. At his school this is especially difficult as it his his given name. The teachers do their best to call him by the name he requests but some of the other children find it difficult to adjust, or even wind him up on purpose (this is an autism unit, not regular school).

As parents we think we need to do something to get him to accept his given name again but really not sure how to go about it. Does anyone have any advice or ideas?

Many thanks

Tom