1. even though agreement was not done on stamp paper, it was acted upon by the parties
2. you also proceeded with the work coming under the scope of franchise
3. so if you directly approach one of their clients without reference to the franchisor, then they would invoke the clauses in the franchise agreement which would take care of the event when the franchisee does something directly with the clients of the franchisor
4. the above may have prompted them to block your payments
5. you need to write to them that no work was solicited from their client by you in your personal capacity and request them to clear your dues
6. if they do not respond to your curtsey letter, then you can issue a legal notice after a week or so
7. then you will have to assess the situation based on their reply
8. eventually you will have to file a suit against them for recovering your dues - a summary suit would be in the anvil because the franchisor has admitted its liability to pay you the amounts under the franchise agreement