Don't see 1130 speed they promising, can't even sustain connection

Got 1gig as previous tenant used it and said it was great. Since last year OCT we started using 1gig which was close to that speed at begining, then got worse following few dropouts, been notified from them this is normal as new line or connection has to settle in. Okay. since then I wasn't been using it much as working till late . Recently the dropouts started again, now more often and longer periods. The speed went from 1130 (which I never seen) to 100 at evenings and 400 mid day  . Were paying £54.4 after April 1 they say averange speed is 1130 . So decided call the support which was nightmare and seemed like scam call center the guy barelly spoke english. Got appointment for technician that came few days after, found zero issues he said, checked cooper cable connections and swaped our line it they green box were he said we would get prioritised signal. After that couble days were fine considering connection, speed wasn't much improved. To conclude how this even allowed? We paying for service we never have? I've had sky for two years in rurral area that never dropout . But this Fibre is worse than 5G in basement.