Cannot then off call forwarding

I ace a couple of iPhones but need to use my iPhone 6. Has SIM card installed.

recently on the iPhone 6 I turned on call forwarding to have one mobile phone receiving calls. I didn’t turn off call forwarding, reset the phone and all settings etc and put in a different SIM card. This SIM card doesn’t seem to revive or send calls or texts. Because of this I put in the inital SIM card and now (even though phone has been reset) the call forwarding is stuck. I cannot turn it off (get an error). I’ve tried calling ##002# and ##021# with no luck. Any other suggestions? This phone appears unusable now with it stuck.