extend virtualbox linux mint partition

After using clone and resize commands of virtualbox I was able to extend a dynamic disk of 16GB to 20 as I wanted. After that I used a debian live ISO with gparted and lvm2 and extended the partition with the allocated space. fdisk though shows error as shown below and df shows allocated space unchanged. Output of fdisk:

sudo fdisk -l

Disk /dev/sda: 21.0 GB, 20971520000 bytes
255 heads, 63 sectors/track, 2549 cylinders, total 40960000 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0000af96

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      499711      248832   83  Linux
/dev/sda2          501758    40959999    20229121    5  Extended
/dev/sda5          501760    40959999    20229120   8e  Linux LVM

Disk /dev/mapper/mint--vg-root: 20.7 GB, 20711473152 bytes
255 heads, 63 sectors/track, 2518 cylinders, total 40452096 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/mapper/mint--vg-root doesn't contain a valid partition table

and df -h:

$ df -h
Filesystem                 Size  Used Avail Use% Mounted on
/dev/mapper/mint--vg-root   12G   11G   29M 100% /
none                       4.0K     0  4.0K   0% /sys/fs/cgroup
udev                       734M  4.0K  734M   1% /dev
tmpfs                      150M  1.1M  149M   1% /run
none                       5.0M     0  5.0M   0% /run/lock
none                       749M  964K  748M   1% /run/shm
none                       100M   12K  100M   1% /run/user
/dev/sda1                  236M   49M  176M  22% /boot
/dev/loop0                 526M   82M  434M  16% /var/cache/openafs
AFS                        2.0T     0  2.0T   0% /afs

Output of lsblk:

$ sudo pvs
  PV         VG      Fmt  Attr PSize  PFree 
  /dev/sda5  mint-vg lvm2 a--  15.76g 24.00m
user@debian:~$ lsblk
NAME       MAJ:MIN RM    SIZE RO TYPE MOUNTPOINT
sda          8:0    0   19.5G  0 disk 
├─sda1       8:1    0    243M  0 part 
├─sda2       8:2    0      1K  0 part 
└─sda5       8:5    0   15.8G  0 part 
  ├─mint--vg-root
           254:0    0   11.8G  0 lvm  
  └─mint--vg-swap_1
           254:1    0      4G  0 lvm  
sr0         11:0    1    1.1G  0 rom  /lib/live/mount/medium
loop0        7:0    0 1008.4M  1 loop /lib/live/mount/rootfs/filesystem.squashfs

Also pvs, lvs and vgs as asked:

$ sudo pvs
  PV         VG      Fmt  Attr PSize  PFree 
  /dev/sda5  mint-vg lvm2 a--  15.76g 24.00m
$ sudo vgs
  VG      #PV #LV #SN Attr   VSize  VFree 
  mint-vg   1   2   0 wz--n- 15.76g 24.00m
$ sudo lvs
  LV     VG      Attr       LSize  Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  root   mint-vg -wi-a----- 11.74g                                                    
  swap_1 mint-vg -wi-a-----  4.00g                                                    

Guest OS I want to extend the partition is Linux Mint with lvm2 filesystem. I have also tried with guidelines from command as https://www.centos.org/docs/5/html/Cluster_Logical_Volume_Manager/lv_extend.html but with the same error message(Disk /dev/mapper/mint--vg-root doesn't contain a valid partition table). What am I missing?