Welcome to the community!
What do you mean by not compatible with your hearing aids? As far as I am aware, all smartphones are required to be hearing aid compatible or HAC (see here). Are you referring to compatibility the Signia App? According to their website, most android devices (Android 5.0 and higher) are compatible with their app. That said, they do list some recommended devices.
When did you get your phone? If you purchased the device recently, Fido does offer a 15-day satisfaction guarantee. I'm not sure what allowances are available if your device is not eligible for the guarantee. You would need to contact customer service to see what are your options. There should be a Live Chat option provided in that link. Alternatively, you might consider sending @FidoSolutions a PM. Once they verify some information, they'll also be able to provide some assistance.
Hope this helps 😀