They cannot re-use a used SIM on another account, as there will be issues with the cancelled Customer A account and the Customer B account.
The same SIM can be used to get a number changed and does not require a new SIM. If you were to call in to request a number change, they can easily do it over the phone, but you'd have to be on a different line (i.e. not the phone that you want the number change on) so that the Rep can make the changes and send the OTA update to the SIM.
The reason most in-store Reps prefer to start with a new un-used SIM to do a number change is it is easier to void out the other SIM and activate the new SIM with the new number in the system. The more experienced Reps will use the same SIM though unless they don't feel like doing it that way.
If you feel that you have to correct some of my posts for my capitalization of some of my words, then just bear with it. It's just a discussion forum where some may be limited by time to answer in well-versed and eloquent sentences.
I already got a PHD (Plain High School Diploma) so ignore my style of writing and I'll ignore your ignorance.
Subject: You can read this-trust me!
I cdnuolt blveiee taht I cluod aulaclty uesdnatnrd waht I was rdgnieg. The phaonmneal pweor of the hmuan mnid. Aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoatnt tihng is taht the frist and lsat ltteer be in the rghit pclae. The rset can be a taotl mses and you can sitll raed it wouthit a porbelm.
Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe. Amzanig huh? yaeh and I awlyas thought slpeling was ipmorantt!
When asked if I see the glass half empty or half full, I responded I see just a glass of water.
Now you know how I think.