There are a few questions:
1. Your factory A and the other manufacturer B have a contract processing relationship, and B sells them under OEM, which is no problem
2 , whether the product or technology covered by the patent he applied for is the product you produce;
1) If so: according to the patent law
An invention-creation completed by the cooperation of two or more units or individuals . For inventions and creations completed by a unit or individual under the entrustment of other units or individuals, unless otherwise agreed, the right to apply for a patent belongs to the unit or individual who completed or jointly completed the application; after the application is approved, the applying unit or individual The individual is the patentee.
Therefore, his behavior of applying for a patent is illegal. He can report it to the local Science and Technology Bureau/Intellectual Property Office, handle it through administrative means first, negotiate with the other party to obtain the right to apply for a patent or become a co-applicant, such as If nothing works, go to court again.
The materials you need to prepare are: the entrustment contract signed with the other party, supply vouchers, product design manuscripts and other vouchers, and the other party's patent application vouchers (patent application number, patent specification, etc.).
2) If not: you cannot protect your rights