How can we erase obsolete back-up sets?

I am with Norton since several years and I changed my hardware quite a few times.  I recently noticed that the back-up sets for PCs I don't own anymore are still in the cloud (taking precious and expensive back-up space).  I just can't find how to delete them.  I contacted Norton support about one month ago and I had a couple of chat sessions with a Norton technician - nice guy - who took control of my laptop, tried this and that for about 45 minutes each time only to tell me in the end that he had to refer my request to the "engineers" or whatever power that be.  Our last chat goes back to 10 - 12 days ago now and still no news.

I am fed up.  

To add insult to injury in the last month I had to renew the subscription for two 10 Go of back-up space that I wouldn't need if these obsolete back-ups were deleted.  More cash in the bank for Norton, I guess.

Can someone help with this deletion problem ?

Thanks

Jean