Legit Win-back promotion offer or Scam?

It's supposedly a valid number for Telus but it's also possible for scammers to spoof their caller ID so it shows they're calling from that or any number. I've never heard of "auto transition" before so that makes me a bit suspicious of the call.

$30 for 100GB seems too good to be true to me. Telus doesn't even have a regular advertised 5G plan that comes close. There is a 5G+ plan on their site for $65/mo that has 100GB of data. That's a sale price also and the regular plan cost is usually $75/mo. I'd be surprised if Telus would offer that for less than half the cost as a win-back. Assuming it was Telus that called you.

I'm doubtful that store reps would have access to win-back offers but you could always ask.