I have exactly the same issue with my new Samsung purchased direct just after release. I use it mainly on my business and home WiFi but had connection issues with my old Telkom SIM since Jan 2021...after lots of back warding and forwarding to Telkom and Samsung I found out MTN (???) blacklisted...
Does anyone else have a major speed loss via CellC on Vuma fibre in the evenings?
paying for 20/20 but upload often drops to 1 to 5 in the evening sometimes even dropping the connection. Speeds tested at the ONT. No response yet from Cell C or Vuma.