DMVPN y OSPF a través de túneles GRE

please help me to resolve the problem with routing between dmvpn GRE tunnels.

I've got a DMVPN HUB and SPOKE topology. HUB has public ip address in internet. SPOKE has two ISPs for redundancy.

I've decided to create two GRE tunnels between HUB and SPOKE for redundancy. I configured GRE tunnels, configured ipsec profiles well. HUB and SPOKE see each other well through this GRE tunnels. But also I'm facing the problem with configuring OSPF between them to provide my topology with redundancy. I've decided to create two OSPF processes (one for each tunnel) and configured networks with different metric values for I have priority between OSPF routes:

OSPF configuration (HUB):

router ospf 100
 router-id 172.20.10.1
 network 172.20.10.1 0.0.0.0 area 0  //GRE TUNNEL IP ADDRESS (1-ST)
 default-information originate always metric 50 
router ospf 101
 router-id 172.21.10.1
 network 172.21.10.1 0.0.0.0 area 0  //GRE TUNNEL IP ADDRESS (2-ND)
 default-information originate always metric 70

OSPF configuration (SPOKE)

router ospf 100
 router-id 172.20.10.13
 network 10.0.13.1 0.0.0.0 area 13  //NETWORK BEHIND SPOKE
 network 172.20.10.13 0.0.0.0 area 0  //GRE TUNNEL IP ADDRESS (1-ST)
router ospf 101
 router-id 172.21.10.13
 network 10.0.13.1 0.0.0.0 area 13  //NETWORK BEHIND SPOKE
 network 172.21.10.13 0.0.0.0 area 0   //GRE TUNNEL IP ADDRESS (2-ND)

As you can see from my configuration I send default route to spoke with different metric values. From SPOKE I send route for network behind SPOKE through both of my GRE tunnels. Also I configured different ip ospf cost values for different tunnel interfaces. Here is the configutaion of my tunnel interfaces.

interface Tunnel100
 ip address 172.20.10.13 255.255.254.0
 no ip redirects
 ip mtu 1400
 ip nhrp authentication nhrppass
 ip nhrp map 172.20.10.1 "HUB IP"
 ip nhrp map multicast "HUB IP"
 ip nhrp network-id 100
 ip nhrp holdtime 300
 ip nhrp nhs 172.20.10.1
 ip nhrp registration no-unique
 ip ospf network point-to-multipoint
 ip ospf cost 50
 tunnel source FastEthernet4
 tunnel mode gre multipoint
 tunnel key 100
 tunnel route-via FastEthernet4 mandatory
 tunnel protection ipsec profile DMVPN100
interface Tunnel101
 ip address 172.21.10.13 255.255.254.0
 no ip redirects
 ip mtu 1400
 ip nhrp authentication nhrppass
 ip nhrp map 172.21.10.1 "HUB IP"
 ip nhrp map multicast "HUB IP"
 ip nhrp network-id 101
 ip nhrp holdtime 300
 ip nhrp nhs 172.21.10.1
 ip nhrp registration no-unique
 ip ospf network point-to-multipoint
 ip ospf cost 70
 tunnel source Vlan1
 tunnel mode gre multipoint
 tunnel key 101
 tunnel route-via Vlan1 mandatory
 tunnel protection ipsec profile DMVPN101

As a result I'm facing some problems with OSPF routes.

I see that both of my default routes from HUB go to SPOKE. If main route (with the better value of metric) is down the backup route is active. It works fine. But I've got the problem with routes on my HUB. I see it recieve only one route to the network behind SPOKE through the first tunnel interface. If this interface is down I don't have backup route to this network through the second tunnel interface.

Please give me an advice, what I do wrong?

Gracias de antemano por cualquier ayuda.