Vodacom Fibre

I have upgraded my WIFI/Fibre line a couple of months ago from 10MBPS to 50MBPS but only have the speed for the first 2 days, afterward it is under 20MBPS and down to 3MBPS. I have escalate/log numerous calls, and however get call back (sometimes), they just sent me a link to take photo's, and sent the proof back to them, NO BODY ever comes back to sort it out, I am paying for actually NO service at all