Holding customers by force

Hi I had a problem with network provider called "Advinne Mobile". I ported my cell c number to "Advinne Mobile" 2 years back. Now I'm trying to go back to cell c from more then 6 months but that network is not allowing me to do so. I even swear the person also. Now they threatening me to open a case against me or sending people to my place to teach me a lesson of complaining and what so ever. There was no contract signed. I'm just on prepaid plan. Any help I can get because that is my business number which I'm not willing to lose or we can sue them?