Hook for expirydate - renew of subscriptions

Hi

I am developing recurring subscriptions for my local payment gateway (not PayPal) and this is a follow up to my previous topic: https://premium.wpmudev.org/forums/topic/payment-gateway-and-recurring-subscriptions

For testing purposes I've made a subscription that will renew/charge some amount every day. When user does a sign-up I'm using my own gateway created as a plugin gateway.mygateway.php and this works fine.

As Membership does not support my (manual) recurrence I'm developing this my self. My problem is that upon sign-up wp_m_membership.relationships.expirydate and some variables in wp_usermeta is set and this effectively stops/cancels the subscription as opposed to my plan of renewing it (my code to charge money to credit card).

If possible can you please provide some advise on what hooks/methods/changes I should make/look for.