Unauthorised change in ISP

I received an unauthorised message and call from Openserve to the effect that there was a change from my current ISP to Gigawave. I instructed Openserve not to change my ISP as I gave no instruction to change ISP to Gigawave. My internet service was disrupted 2 days later and has remained unavailable for a week with no prospect of resolution in sight. My current ISP has been waiting for a response from Openserve for a week, but the problem had been initated by Gigawave. Gigawave has done nothing to resolve the problem that they created, they do not have a call centre number that I can call and they ignore my instructions to fix the problem on their whstsapp helpline and website support chat service