Recurring contribution (monthly) with 'Pay Later'
This extension solves your use case and was designed for that purpose and several other related ones:
https://github.com/adixon/ca.civicrm.contributionrecur
For example, you can track recurring offline payments (whether by bank transfer or other form of recurring payments that don't have a civi extension) by configuring it to auto-generate contributions for those offline payments. Then you just have a monthly reconciliation task to weed out the ones that didn't go through.
It supports both credit card and bank transfer offline recurring payments (using separate 'placeholder' type payment processors).