We can only address the question at a general level, and you'd need to hire an attorney to get an answer tailored to your circumstances. Also, there isn't enough information available to us about your relationship with Block.
Presumably, you have some kind of client agreement with the company, which will say things about what they will and can do, and likewise for you. That agreement will be the primary source of privacy-related restrictions on what they can do w.r.t. you. If "you" (the account holder) are defined as being you and your ex-wife, then they cannot deprive your wife of her contractual right to access to information. It does not matter that you are now divorced: what matters is what is in the agreement. It is highly likely that her access to this information is based on her being a party to the contract. There is a tiny chance that this is due to a screw-up on their part, such as them typing in the wrong ssn when modifying an account or creating a new account.
The document you link to regarding privacy policies is just one of many – they provide 4 other links applicable to other client relations. That document tells you what information they collect, there they get it from, what they do with it and who they share with. For example they say they do not sell your information. The applicable promise in this document seems to be:
We do not sell, or rent your information (including your social
security number). We may share your information to support the
products and services you request or provide you information on
products and services that may benefit you. We may also share your
information as permitted by law or with your additional consent.
This does not preclude freely sharing information in a way that is allowed by law. 26 USC 6103 is relevant law. The general rule is that returns are confidential and cannot be disclosed if obtained by certain people in connection with service as an employee acording to provisions of that section. In particular,
(3) no other person (or officer or employee thereof) who has or had
access to returns or return information under subsection
(e)(1)(D)(iii), subsection (k)(10), paragraph (6), (10), (12), (16),
(19), (20), or (21) of subsection (l), paragraph (2) or (4)(B) of
subsection (m), or subsection (n),
Section (e) is about permitted disclosures to persons having material interest. That section starts by saying that that is
(A) in the case of the return of an individual...(ii) the spouse of
that individual if the individual and such spouse have signified their
consent to consider a gift reported on such return as made one-half by
him and one-half by the spouse pursuant to the provisions of section
Thus they are allowed to disclose your return to your wife. It does not matter whether you file jointly or separately. What does matter is whether she is your spouse.
If they disclosed a return for a tax year where you were not married (and she had none of the other listed interests), that might be a violation of the law. For the most part, this law restricts government disclosure of tax returns, but there is that clause applicable to all employees. Your attorney would then scrutinize that extremely long section to see whether such a disclosure is illegal, and whether there is some escape from liability if you fail to notify the company that X is no longer your spouse.
You need an attorney to solve your problem. If you are just curious as to how the law works, that is why we are here, but it's impossible to say anything useful without details on how she got access, and what your agreement states.