Default can't connect to 3g

hey guys i'm having an issue where i can't connect to 3G (GSM)
when i change it to GSM i get bars (no icon & no data) and my phone says just says searching where it should show the carrier, i've tried 2 different sims (wind & bell) both do the same thing

bell sim works on LTE and 4G (WCDMA) but not 3G (GSM)
wind sim works on 4G (WCDMA) and nothing else

anyone have any ideas why 3G (GSM) isn't working for me?