what i understand is, the RM50 u paid when u sign up is consider as "advance" and to offset first month bill, but you are still require to pay RM50 in the first month bill to offset second month.

or you just think like that, RM50 is deposit, so first month will still bill you RM50++, when you terminate the account, deposit will be refunded to you in 3 months

correct me if i am wrong

but not sure why you got RM110, you sign up 2 GX50 line?

I think you got the wrong info.
Your RM50 paid is a deposit for the plan you subscribed.
Then, you'll need to pay for the first month RM50 with 6%  SST + RM10 stamp fee (one-time). Therefore, it's RM60+.
The RM50 you paid at the time of subscribing is actually used to offset your LAST bill (porting out or termination) with balance credited back to your bank. You'll need to update your bank account no.