Connecting Asterisk with a legacy PBX

I’m trying to connect Asterisk with our existing PBX system (quite an old one), but for some reason inbound calls from from the PBX are not showing any calling or called numbers and appear on CLI as:

-- Accepting call from '' to 's' on channel 0/30, span 1
-- Executing [s@pbx-index:1] Answer("DAHDI/i1/-1", "") in new stack
-- Auto fallthrough, channel 'DAHDI/i1/-1' status is 'UNKNOWN'
-- Hungup 'DAHDI/i1/-1'
-- Accepting call from '' to 's' on channel 0/31, span 1
-- Executing [s@pbx-index:1] Answer("DAHDI/i1/-2", "") in new stack
-- Auto fallthrough, channel 'DAHDI/i1/-2' status is 'UNKNOWN'
-- Hungup 'DAHDI/i1/-2'

If I try to dial any legacy PBX extensions form a phone registered to Asterisk everything is working fine, but not the other way around.

I will appreciate any help.

Below few more information:

Description Alarms IRQ bpviol CRC Fra Codi Options LBO
Wildcard TE131/TE133 Card 0 OK 0 0 0 CCS HDB3 CRC4 0 db (CSU)/0-133 feet (DSX-1)

dahdi show channels
Chan Extension Context Language MOH Interpret Blocked In Service Description
1 pbx-index default Yes
2 pbx-index default Yes
3 pbx-index default Yes
4 pbx-index default Yes
5 pbx-index default Yes
6 pbx-index default Yes
7 pbx-index default Yes
8 pbx-index default Yes
9 pbx-index default Yes
10 pbx-index default Yes
11 pbx-index default Yes
12 pbx-index default Yes
13 pbx-index default Yes
14 pbx-index default Yes
15 pbx-index default Yes
17 pbx-index default Yes
18 pbx-index default Yes
19 pbx-index default Yes
20 pbx-index default Yes
21 pbx-index default Yes
22 pbx-index default Yes
23 pbx-index default Yes
24 pbx-index default Yes
25 pbx-index default Yes
26 pbx-index default Yes
27 pbx-index default Yes
28 pbx-index default Yes
29 pbx-index default Yes
30 pbx-index default Yes
31 pbx-index default Yes

dahdi_hardware
pci:0000:07:00.0 wcte13xp+ d161:800a Wildcard TE131/TE133

system.conf
span=1,0,0,ccs,hdb3,crc4
bchan=1-15
dchan=16
bchan=17-31
loadzone = uk
defaultzone=uk
echocanceller=hwec,1-15,17-31

chan_dahdi.conf
[channels]
context=pbx-index
switchtype=euroisdn
signalling=pri_net
usecallerid=yes
cidsignalling=v23
callwaiting=yes
usecallingpres=yes
sendcalleridafter = 2
callwaitingcallerid=yes
threewaycalling=yes
transfer=yes
canpark=yes
cancallforward=yes
callreturn=yes
echocancel=yes
echocancelwhenbridged=no
group=1
callgroup=1
pickupgroup=1
progzone=uk
channel => 1-15,17-31