They have to hit their secret target for manufacturing e-waste somehow, & they've found a method which also causes their customers hassle, knowing VM they doubtless consider this a bonus.
Best of luck sorting the numbers out, I'm not sure if PAC codes work when you're not actually changing provider, STAC codes to just cancel a number for sure don't, at least, not with Virgin. I think the plan is to make it difficult enough you end up paying for two SIMs rather than jump through the hoops to cancel the not-needed one.