Not sure if anyone replied, but I'll answer this.
1. Yes, payment for SuperRoam MY is every 90 days. There is no 30 days option.
2. Yes, every 30 days your data/call minute/SMS allowance will be refreshed to 130GB/10GB/etc.
3. If you don't want your phone number, just email them this form(
https://www.simba.sg/static/media/Account-Termination-Acknowledgement-Form 02032022.a37ea02e.pdf) to terminate/don't make payment at all (but it will keep trying to charge your credit card every day for about 1 month straight). If you still want your phone number, just port out to another telco about a week before the next renewal to prevent getting charged the following month. (++ If you port out within 30 days of plan activation, you will get charged an additional $30)