I recently ported my on account VF number to Kogan on mhy OnePlus 9. The porting was a bit tortuous but appeared to work.

But now it seems that SMS to VF phones shows the original 028 number but to other networks it shows the right number.

Calling shows the right number.  Contacted Kogan support who said try another phone so I tried a different phone and it's fine. So it appears to be a problem with my Oneplus 9 but I cannot find any setting where it sends a different number to only a specific carrier.

Any ideas?