Ventresca how old is the 'old' phone? The fact another SIM works in it, and I imagine is in the same locale, would imply that the device is not banned due to the IMEI as this normally occurs across operators in a given area from a centralised database.
I would ask for your number to be ported to a replacement SIM, this can usually be done in a store if you have one nearby to reduce service down time otherwise, it may require sending one to you via your carriers process.
I'd been with my carrier since the early 2000s and as the 4G network was rolled out some older SIMs would no longer work or pick up 4G requiring an upgraded SIM. This may be the case here either that or your older phone SIM tray could have different tolerances than the Pixel 7 in regards the metal springs that touch the different SIM elements etc.