Casa Plumbers geyser experience

Had a issue with my new geyser that was installed by CASA plumbers after 3months then, they informed dew to the old pipes the rust is causing the geyser pipe to get blocked. It worked fine for one month and then again on and off but non of the other flats before me are having the issue. The more I'm informing them that there is something wrong with the geyser they are insisting that it is the rust. I asked them to come out and see to install a filter before the geyser in order for us to check and see if there is any rust coming through and still have not heard from them since last week.