Vodacom Fibre 50/5 ****

I migrated my home fibre from 10/10 to 20/2 to 50/5 , the 10/10 was stable and never had a issue with the Data transfer Speeds and stayed at required speed .The 20/2 migration was also a good transition with 20/2 being stable at required speed. I then stepped the line up to 50/5 migration , this was the problem , ever since the migration the line is unstable with as little as 10mbs to 38mbs on download with the upload stable at 5mbs. I was contacted by Vodacom to connect my PC directly into the line to "get the correct Speed " using a link provided, this was done and best result achieved was 38mbs .This was sent to them and they received this. When checking later the line was unstable with results of 10/15 and 20mbs download speed. I have numerously contacted the *** line with no success , I have been numerously disconnected whilst on the line as well .It is frustration to get a simple thing like this sorted , I wonder if a person could get what is requested ,and what one pays for