Don't blame this on "Payment provider"/"Payment Facilitator, simply get a new PF if the current PF creates problems. Mastercard and Visa are bad but as far as I know are only trying to enforce USA style "child porn" laws on foreign countries (yes they are that bad). MC and Visa have not banned adult contents, this is an issue with the current PF, see GBPP (Global Bran Protection Program or such), BRAM (Brand Recognition ...) programs by Visa/MV to see what MC and Visa officially currently accepts. What MC/Visa accepts if more or less -> local law - CP unless CP ban breaks local law (probably).
Finding a new PF should fix the issue, and there should be many PFs out there that do adult contents, especially contents not featuring actual real people like drawn images. I can try to see if I can find a PF to give ITCH a call but this situation is the fault of ITCH not finding an alternative PF, and mostly not the fault of MC/Visa.
That being said there is a lot of unofficial rules implemented by PFs but those should be possible to navigate by ITCH.