Trademark rights are both acquired and maintained by use, so if the user stops using the TM and intends to abandon the rights, they become available to other users. If the company you used to work for is no longer in business, you wouldn't need them to release rights to you, and if no one else since their use has used the trademark, it's available for your use and registration. But if the TM was cancelled, and didn't simply expire, then that means another user successfully challenged your former company's use and got the USPTO to cancel their rights, so there is, or was, some other user out there.
See an IP lawyer to see if you can try to register the same TM that your former company got, or to see who and what else is out there who beat you to the rights.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
In addition to the foregoing, it's best to think of a trademark (for goods) or a servicemark (for services) relative to the mark's underlying goods and services.
If your business will be doing something different from the defunct company (or anyone else using a similar name or mark), that difference weighs in your favor. In other words, if the old company was named XOPOS and was using XOPOS as a mark for running shoes and now you want to use XOPOS to sell computer services, you're probably OK since the goods and services are so different and are likely sold in very different trade channels.
However, you should consult an intellectual property attorney to formally "clear" the desired mark since there are many variables not addressed here (e.g., "fame" of the same or similar marks in use, continued common law usages, etc.)
Best of luck.