if they advertised it as unlocked then i would contact them to return it for one that is. TMO wont be able to unlock it unless you are the original purchaser and have met all the criteria needed.

Unlock eligibility requirements

We unlock mobile devices that meet the following eligibility criteria free of charge.

Device eligibility is determined as follows:

• The device must be sold by T-Mobile.
• The device must not be reported as lost, stolen or blocked.
• The account associated with the device must be in good standing.
• The device must also satisfy all the Postpaid or Prepaid unlocking requirements outlined below.

Unlock eligibility for mobile devices on Postpaid plans

• The device must have been active on the T‑Mobile network for at least 40 days on the requesting line.
• If the device was financed or leased through T‑Mobile then all payments must be satisfied and the device must be paid in full.
• If the device is associated with a canceled account, then the account balance must be zero.
• T‑Mobile may request proof of purchase or additional information in its discretion and certain other exceptions may apply.

Unlock eligibility for mobile devices on Prepaid plans

• At least  365 days  must have passed since the device was activated on the T Mobile network.
• If the device was activated less than 365 days ago, then the   Prepaid account associated with the device must have had more than $100 in refills during that period for each line active on the account.  In   addition, more than 14 days must have passed since the device was purchased.
• No more than 2 mobile device unlocks have been complete per line of service in the last 12 months.
• T‑Mobile may request proof of purchase or additional information in its discretion and certain other exceptions may apply.

To be eligible for a SIM unlock, you must be a T-Mobile USA customer and meet all of the SIM Unlock Policy requirements.

https://www.t-mobile.com/responsibility/consumer-info/policies/sim-unlock-policy

You could always try a third party unlocking service from a cellphone repair place.