Pathetic fibre speeds

Since Telkom sms'd us to say that from the 1st May 2020, they are doubling our 10 mb/s fibre line, free of charge, to a 20 mb line during the lockdown, our speed has been at best dismal. We used to get about 4 or 5 mb/s average download speeds on the 10 mb fibre, we now often get less than 1 mb/s!!