Apple Cash is operated by Green Dot Bank and they have to follow the rules that congress approved with the Bank Secrecy Act and the Patriot Act. It is illegal for the bank to give you any information about an investigation or even if an investigation is going on. The contact person you talked is not even given any information that could help you as there is nothing they can do either. Apple is not involved at all and it would be illegal for them to interfere in any of the banking regulations.
I can give you more information about the Bank Secrecy Act and the rules that banks must follow, but it will not change any of the decisions that were made and changing the rules that the banks must follow would require an act by congress.
To be clear is is not your Apple Pay that has been restricted, it is Apple Cash.