B I N G O ! ! !
That’s exactly what happened.
This is the downside of Amazon. They don’t clean their inbound customer-return inventory thoroughly, this has happened to me only twice before with filament. But consider the 50ish spools I’ve purchased since last August and that isn’t exactly a bad thing given the no-hassle return policy.
You probably got the spool I sent back last month.
But seriously, I’m sure you already know this but for the benefit of others.
If you haven’t already done so, send it back now for an exchange, not a credit. The reason for the exchange is that you’ll receive credit right away, and an advance shipment will be sent at no charge. You’ll then have 30 days to return the product at their expense.
If you live in the US, the best option I’ve found is UPS option where you print the label and supply the box(usually the box it came in or some other Amazon envelope). Repack the item in the original box and you’ll find that a spool box fits perfectly in any UPS drop box. By 5:30 PM, they’ll pick it up, and by 7 PM, you’ll receive your credit.
Alternatively, you can also drop it off at an Amazon unattended Locker(you supply box and label), Whole Foods, or a UPS store, where they’ll pack it for you if you don’t have a box or label at no charge to you. At the UPS store, you receive a receipt right away too, and the credit appears quickly on the Amazon app(generally within 10 minutes to four hours).
UPS – best Amazon return option in the US in my experience.
I’ve tried UPS Store drop-offs, Staples drop-offs, and Amazon Lockers. The UPS self-label and self-pack option I find to be the best because if the box doesn’t fit in a UPS drop-box, I can go take the package to the nearby UPS store to hand it in and get a receipt. It’s a little further drive and I have to do it during their 8AM-6PM Mon-Sat business hours.
Consider this a happy accident.
Summary
If you haven’t ever returned a partial spool, you have an opportunity to test the return process on a said spool. If it were new and unsatisfactory, you might have kept it, but now there’s no reason to.
This is one of many reasons why Bambu hasn’t received a spool order from me since last summer. After they ran out of basic PLA colors such Black, Grey, and White, I was forced to source filament elsewhere. I’m grateful that they showed me the way. 
Their loss, my gain.
Are you listening Bambu? If you hadn’t stocked-out for weeks, not knowing any better, I would likely have remained your filament customer! But you forced me to find alternatives, THANK YOU!!!
To those who are still buying from the mothership out of fear of the unknown and who are NOT AMS users.
Summary
I was initially hesitant about Amazon suppliers, but with their liberal return policy, trying new suppliers became a fun adventure. Ever since, I’ve been hunting for that elusive $10 PLA that performs well and is consistently available at that price. So far, my best finds are in the $13-14 range. But I have to be flexible because pricing isn’t always the same. That’s why I have a big library of tuned filament profiles. Now it’s become much easier to switch brands. As a result, I feel empowered to switch suppliers at a moments notice if a flash deal pops up or someone jacks up their cost like Overture and PolyMaker frequently do.
Contrast that that against Bambu’s substandard filament quality, 2x-3x the price, bad return policy and course they charge for shipping that might get to you in 6-10 business days. What’s not to like? 
But seriously, unless you have an AMS and need the fancy spool, there is zero reason I have been able to come up with to justify the purchase of Bambu filament. I baffles me why more people don’t just take the plunge and go elsewhere.
I return about 10% of the spools I buy on Amazon if they don’t meet the manufacturer’s claims, and I’ve never been denied.
Example Proof
Summary
Here’s a picture of two such spools from Fremover PLA that after consuming 200g(20%) of each spool, I could not get it to tune no matter what. Fremover tech support ignored me. So on day 20 of the 30 day return window, I returned the spools with 20% already consumed. I got my money back, no questions asked.
