DGN2000 force ADSL2+

Hi everybody,
after upgrading my ADSL line to 20M my ADSL line is too slow.
I have contacted my ISP which says that the cause of such slowness is the modulation of my router that is set to ADSL2 instead of ADSL2+.
From the router gui I don't have this setting so I connected with telnet to my router.
These are the actual settings:
multiplexing method --> LLC Based
VPI --> 8
VCI --> 35
Encapsulation --> PPPoE

I have the latest firmware version: V1.1.11.0

How can I force ADSL2+ settings?

Following are the stats of my router:

# adslctl info --show
adslctl: ADSL driver and PHY status
Status: ShowtimeRetrain Reason: 8000
Channel: FAST, Upstream rate = 468 Kbps, Downstream rate = 4407 Kbps
Link Power State: L0
Mode: ADSL2
Channel: Fast
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 9.9 8.8
Attn(dB): 23.0 12.3
Pwr(dBm): 18.5 12.6
Max(Kbps): 5728 476
Rate (Kbps): 4407 468
G.dmt framing
K: 138(0) 14
R: 0 0
S: 1 1
D: 1 1
ADSL2 framing
MSGc: 59 17
B: 137 13
M: 1 1
T: 1 3
R: 0 0
S: 0.9945 0.9333
L: 1110 120
D: 1 1
Counters
SF: 2781587 2809828
SFErr: 544 5515
RS: 0 0
RSCorr: 0 0
RSUnCorr: 0 0

HEC: 428 3523
OCD: 63 0
LCD: 0 0
Total Cells: 467352459 583201555
Data Cells: 28787775 8255521
Drop Cells: 0
Bit Errors: 0 308585

ES: 397 1926
SES: 0 37
UAS: 36 1511436
AS: 44957

INP: 0.00 0.00
PER: 16.16 16.10
delay: 0.24 0.23
OR: 32.17 11.42

Bitswap: 1227 255

Please help, it's two months I'm getting crazy with my ISP!

Thanks in advance,
Tarek