WiFi and LAN Speed is not consistent with Paid Package

I am a client with a 100/100 Mbs fiberline with the company. my LAN connection is giving me satisfactory results with both download and upload speed. but as soon as a device is connected via the ONT's WiFi the speed drop to a unsatisfactory speed. I can not access the UI interface of the Huawai router due to the fact that the company has blocked any access to the UI by the clients. When ever I contact with the Service department they test the line and say there is no problem. I am using the line for special Work from Home projects and need the WiFi up and down speed consistent at at least 75% the same as the LAN speed. At this stage the company has a monopoly in the area as the only fiber supplier, and I am getting the impression that they do not realy care about client satisfaction and do not want to resolve the issue that I am having.