Take one step at a time..... I assume you have a smart phone. I will suggest you download the following phone application and start recording his calls. Make sure you put your phone on SPEAKER whenever your husband calls b'se this application will then record his voice very clearly.
Then see if your husband, in-laws & your parents and few of your other relatives come together for a meeting. Play this recorded calls and then try to settle this matter amicably....
If this doesnt work go and file a police complaint, you might want to take help by calling women's help line or an NGO before going to police station.
This should stop the harassment for sure........