diff --git a/sessionmanager/smg_event.go b/sessionmanager/smg_event.go
index be0d319a7..0e710418c 100644
--- a/sessionmanager/smg_event.go
+++ b/sessionmanager/smg_event.go
@@ -165,7 +165,11 @@ func (self SMGenericEvent) GetLastUsed(fieldName string) (time.Duration, error)
 	if fieldName == utils.META_DEFAULT {
 		fieldName = utils.LastUsed
 	}
-	result, _ := utils.ConvertIfaceToString(self[fieldName])
+	valStr, hasVal := self[fieldName]
+	if !hasVal {
+		return nilDuration, nil
+	}
+	result, _ := utils.ConvertIfaceToString(valStr)
 	return utils.ParseDurationWithSecs(result)
 }
 
diff --git a/sessionmanager/smg_session.go b/sessionmanager/smg_session.go
index 7d6238ec5..fc0032821 100644
--- a/sessionmanager/smg_session.go
+++ b/sessionmanager/smg_session.go
@@ -41,6 +41,7 @@ type SMGSession struct {
 	sessionCds    []*engine.CallDescriptor
 	callCosts     []*engine.CallCost
 	extraDuration time.Duration // keeps the current duration debited on top of what heas been asked
+	lastUsage     time.Duration // Keep record of the last debit for LastUsed functionality
 }
 
 // Called in case of automatic debits
@@ -52,7 +53,7 @@ func (self *SMGSession) debitLoop(debitInterval time.Duration) {
 			return
 		default:
 		}
-		if maxDebit, err := self.debit(debitInterval); err != nil {
+		if maxDebit, err := self.debit(debitInterval, nilDuration); err != nil {
 			utils.Logger.Err(fmt.Sprintf("<SMGeneric> Could not complete debit opperation on session: %s, error: %s", self.eventStart.GetUUID(), err.Error()))
 			disconnectReason := SYSTEM_ERROR
 			if err.Error() == utils.ErrUnauthorizedDestination.Error() {
@@ -75,7 +76,17 @@ func (self *SMGSession) debitLoop(debitInterval time.Duration) {
 }
 
 // Attempts to debit a duration, returns maximum duration which can be debitted or error
-func (self *SMGSession) debit(dur time.Duration) (time.Duration, error) {
+func (self *SMGSession) debit(dur time.Duration, lastUsed time.Duration) (time.Duration, error) {
+	if lastUsed != nilDuration &&
+		self.cd.DurationIndex != 0 &&
+		self.lastUsage != lastUsed {
+		if self.lastUsage > lastUsed { // We have debitted more than we have used, refund in the duration debitted
+			dur -= self.lastUsage - lastUsed
+		} else { // We have debitted less than we have consumed, add the difference to duration debitted
+			dur += lastUsed - self.lastUsage
+		}
+	}
+	self.lastUsage = dur // Reset the lastUsage for later reference
 	// apply correction from previous run
 	dur -= self.extraDuration
 	self.extraDuration = 0
diff --git a/sessionmanager/smgeneric.go b/sessionmanager/smgeneric.go
index f9e4e27a7..8da95aa45 100644
--- a/sessionmanager/smgeneric.go
+++ b/sessionmanager/smgeneric.go
@@ -167,18 +167,20 @@ func (self *SMGeneric) GetLcrSuppliers(gev SMGenericEvent, clnt *rpc2.Client) ([
 
 // Execute debits for usage/maxUsage
 func (self *SMGeneric) SessionUpdate(gev SMGenericEvent, clnt *rpc2.Client) (time.Duration, error) {
+	evLastUsed, err := gev.GetLastUsed(utils.META_DEFAULT)
+	if err != nil {
+		return nilDuration, err
+	}
 	evMaxUsage, err := gev.GetMaxUsage(utils.META_DEFAULT, self.cgrCfg.MaxCallDuration)
 	if err != nil {
 		return nilDuration, err
 	}
 	evUuid := gev.GetUUID()
 	for _, s := range self.getSession(evUuid) {
-		if maxDur, err := s.debit(evMaxUsage); err != nil {
+		if maxDur, err := s.debit(evMaxUsage, evLastUsed); err != nil {
 			return nilDuration, err
-		} else {
-			if maxDur < evMaxUsage {
-				evMaxUsage = maxDur
-			}
+		} else if maxDur < evMaxUsage {
+			evMaxUsage = maxDur
 		}
 	}
 	return evMaxUsage, nil