You have no other option but to submit this client declaration that they do not issue any such letter.
Rest is up-to the visa officer to decide as to what they want to do. I cannot really say what decision he will take. Embassy may try to validate the end client job and work via other means or other paperwork that you submit.
Hi Kumar,
Even I am in same position my client wont provide and i lost my job during this covid. I received a mail from chennai asking for latest client letter. dont know what to do