Replacement SIM apparently activated but not working

I recently lost my phone ( including the SIM card) and ordered a replacement SIM as well as a SIM-free phone, after blocking the old phone and SIM card. The new phone is working perfectly, and also recognises the SIM when it is inserted. I have activated the SIM using my online ID mobile account, and received a message saying that my new SIM card had been activated. However, 24 hours later I have no network, cannot make calls, and cannot use data. My area has very good 3G/4G coverage, and I have cleaned and re-inserted the SIM card many times. When looking in my phone settings, the number is unknown, the network has no service, and the mobile network type is unknown. I have unblocked the SIM card, do I also need to unblock the old phone? I assumed that since that device is lost it would be unwise to unblock it.