Your ISP may be correct. You need to take into account what those statistics are measuring. RIght above those graphs is the current destination:
By default it measures to Google DNS, which is an anycast address somewhere out on the Internet. The loss may be happening anywhere between you and Google, which may or may not be inside your ISP's network.
If you go to the Security & SD-WAN > SD-WAN & traffic shaping page you can set additional test destinations under the Uplink Statistics section.
Try adding your ISP's gateway, or your ISP's DNS servers. Or do a traceroute to 220.127.116.11 and add every hop in the path. Once you have more destinations you can see if there's loss to some destinations and not others. If you have no loss to your gateway then your ISP is right in that your service is fine. If you do have loss to your gateway then I'd get back on the phone with them and give them heck 🙂