New SIM not working

I have transferred my old number to the new SIM card. I inserted the card into my phone, it was activated, and I received the confirmation email. At first, I was able to connect to the internet, but I could make or receive phone calls and texts. I switched off my phone hoping that this would resolve the issue, but now I'm not able to connect to the internet either. My phone recognises that the SIM belongs to SMARTY, but it says "No connection". I've been trying to resolve the issue following the videos, I've edited the Access Point names, I tried all the suggested hacks, and it still doesn't work. HELP, please!!!