I been a $15 prepaid plan customer for many years. They changed it to $18 more recently buy they did give a bit more from original plan like unlimited call and sms and also 250mb 4g data. It is similar to the current $15 plan but you get unlimited call and 4g speed.
I don't mind paying the extra $3 for peace of mind unlimited call.
Also I noticed each prepaid plan number/account has to have a separated credit card associated to the account. Is there anyway to set the same card.