Use t-mobile home internet and spectrum concurrently

I overlapped for a couple of weeks so that I could take my time switching all my devices over to t-mobile. My final switch was replacing my router with a switch for my ethernet. Then with nothing left on Spectrum, I pulled the plug on the cable modem and called to cancel Spectrum. Retentions noticed my modem was disconnected and that I was ready to leave and so didn't hassle me much with new offers.