Pls refer to the advice of Mr. Sudhir Kumar.
The circular regarding notice period of 3 months is issued by whom, consultant or Company where you were located?
If circular is issued by company it should not be applicable to you, since you are neither employed by company nor your salary is paid by company.
Since offer letter is employed by consultant, it can be implied that consultant has seconded you to company.
However it shall be appropriate to visit your lawyer with all records in person.
You may post copies of letter, salary payment record e.g. bank statement/salary slip, circular in the forum. You may erase the names etc to maintain the confidentiality.