Can you see if interleaving is on? If so then it typically takes between one and three weeks for it to swap it to G.INP and give you back your higher sync. As far as I know there is nothing the ISP can do about it.
Kindness isn't going to cure the world of all its awfulness but it's a good place to begin. Daisy Ridley.
My broadband basic info/help site - www.robertos.me.uk.
Domains, site and mail hosting - Tsohost
Connection - AAISP Home::1 80/20. Sync 59500/14989kbps @ 600m. - BQM