私もAT&Tにロック解除できんと言われたので、今しがたMSサポートとコンタクトした
対応してくれるそうで、以下やり取りの転記

私：hi
MS：Hi! Thank you for contacting Microsoft Surface Support, I hope you are having a great day so far.
MS：Before we start, may I have your first, last name, phone number and email address associated to your Microsoft account? Just in case we lose connection.
私：my name is　私. e-mail:私@gmail.com
MS：Thank you! Just for you to know, this is the case number we are going to be working on: 1032000521, additionally, If you experience any disconnection from your or my end, do not close the chat window, since I will call you If we are not successful to resume the interaction within 5 minutes.
MS：You can always contact us back using the following link: https://support.microsoft.com/contactus
MS：What can I do for you today 私?
私：i bought surface duo(condition:new, at&t locked version) from amazon.com.
私：i contacted at&t two weeks ago, and tried to unlock it.
私：however, i received the following message...
<The manufacturer doesn't have an unlock code for this device.
Device IMEI number: 一二三四五六七八九十
Request number: NUL一二三四五六七八九十>

私：i bought a new surface duo. why can't unlock it?
私：there seem to be many examples that microsoft unlocked it. will you support me?
MS：Thank you for bringing to my attention that  you need to unlock your surface duo, I understand the importance of having your device fully unlocked, you can rest assured I will take care of this today.
MS：May I have the serial number of your Surface, please? On your Home screen, tap Settings.
MS：In Settings, tap About / Model & hardware, and look for your Serial number.
MS：This is the quickest way to find your serial number.
私：please wait a moment.
MS：Sure thing!
私：my serial number is 一二三四五六七八九十
MS：Fantastic, thank you! That will make my request of the unlock code a lot easier. Do you mind if I ask you a couple of questions? For the case notes.
私：yes.
MS：1.Just to be sure, besides that email, you haven't received any other email from AT&T, correct?
私：yes.
MS：Understood, I will proceed to submit the request from my side, can you please allow me 2 minutes?
私：thank you!
MS：Glad to help! In the meantime, if you don't mind me to ask, what type of work are you planning to do with the surface duo? Will be for entertainment perhaps?
私：and business.
MS：Oh I see, I know that the surface duo will be a great fit for you and your business thanks to the dual screen! The request has been submitted, it will be ready in the next 5 business days, and I will send you a follow up email at the end of our interaction with some tips on how to get the max from the dual screen for your work, I know you will find them useful! Once the unlock code is ready I will personally send it to you over email.
私：thaaaank you verrrry much!! im wainting for you!!
MS：You are very much welcome!! Just a quick recap, we resolved this situation by submitting the request from our side and by opening a communication channel over email with you, I will be sending you an email so you can get in contact with me regarding this case.
MS：Is there any other situation I can resolve for you today?
私：nothing, thank you!
MS：Great! Just for you to know, you might be receiving a closing email regarding this chat. Please remember we have your case open for communication via email. I will be glad to provide any required follow up regarding this case.
MS：Before you go, you will be given the chance to rate the level of satisfaction about the service provided today. Thank you for contacting Microsoft Surface Support. Have a great day and stay safe