Fibre totally unstable for past month or longer

We made 12 calls over the past 25 days to the call center with no lasting improvement. The staff were always friendly, helpful and patient, but the internet service stayed unacceptable. We were advised to replace our modem, to no effect. A technician came yesterday at last, and everything was fine, but a few hours later we again had no connection since 5 pm yesterday.

A lady followed up this morning and said she would report our problem to the manager, but nothing happened since.