Bad after service on geyser claim

I had a geyser claim in February 2025, they came and repair it, but after that, my pipes is making a huge noice, the water pressure is very low, and I dont get warm water in the kitchen. We called Standard bank they opend a complaint, but the lady working with this is not coming back to me. The service supplier who fitted the geyser, contact number does not exsist. Every time I call Standard bank let me hold on for 10 to 20 min. Either the line cut or they transfer me, and the 20 min start over.. I have been following this up for six months now. The geyser was installed incorrectly, and Standard bank is not getting back to me. What do I need to do, to get the service I deserve? Please just help me.