It may be that they're waiting for the old equipment to be sent back - for testing or in general - and new to be despatched soon after. It's difficult to tell.
All is sure, though, that your WiFi problem is linked to your environment, especially if a number of BT hubs have not resolved the issue for you. I'd therefore start focussing on your environment to identify the issue.
In particular, older devices, devices that are not properly configured, or devices that have malware on them can be an issue. Additionally, WiFi congestion (on the same channel) may also be a problem. Finally, using a VPN style connection can slow down your connection, not to mention anything being streamed or downloaded in the background. Possibilities are endless. In my household, for example, the WiFi is lightning fast normally but someone in the neighbourhood has an electrical device (electric fire or blanket, as the issue mainly occurs in the winter) that slows down everything (through imposing noise on the mains) when it's on. Even though it was classed as SHINE by Openreach Chief Engineer's office when they came out here to do tests after 20+ Openreach engineer visits, it's difficult to eliminate and it can even affect you when you're on full fibre.
If course, the best way to test your connection is by using an ethernet connected device to confirm that the speeds you're getting are the speeds that you had signed up for. Then to have a methodological approach - by switching off everything that uses your connection and starting from scratch.
Without more details, it's difficult to tell.
