Dear Mr. Hemant,
You can use Public API like "View and Track Returns" which will give response of all return filed by TaxPayer in provided Financial Year. From this also you can understand the frequency of filing of GSTR-1 and GSTR-3B of TaxPayer.
Presently GSTN released specification for Save Preference and Get Preference only in Sandbox and Not in Production. If you are using decrypted API then you can check it in Sandbox.
TaxPro GST API Library dll will be released ASAP for Sandbox Testing of same.
Thanks & Regards
TaxPro GSP Team