Openserve gone bad

What can I say. I stay In Rietvalleipark area Pretoria. Openserve visited a couple of times to come an view the low internet speed they deliver. The box number RYP B9. As soon as they visit. They internet connection is stable. Ruffly after 5 days the internet speed Plummets. This has happened on several occasions. If asked, what should be done if the problem arises again. Openserve reply :" you should called again." With no real solution.