Dig from a specific domain shows no answer but normal dig works

Question

I am having an issue with a WHM installation that was done over a week ago. It seems all is good on the WHM side of things but I am having issues with my nameservers I have set up

Whenever I try to change a domains nameservers over to mine it rejects it(ns1.iclixhosting.co.za, ns2.iclixhosting.co.za)

I have called around the different providers and it seems it is ns2 that is giving the problem

When I run a dig command it returns an A record

dig ns2.iclixhosting.co.za

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-26.P2.el7_9.3 <<>> ns2.iclixhosting.co.za
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 8738
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;ns2.iclixhosting.co.za.                IN      A

;; ANSWER SECTION:
ns2.iclixhosting.co.za. 3252    IN      A       164.160.80.20

;; Query time: 304 msec
;; SERVER: 9.9.9.9#53(9.9.9.9)
;; WHEN: Wed Feb 17 15:36:59 SAST 2021
;; MSG SIZE  rcvd: 67

However what they are saying is that they do not pick it up when they try run it through the specific domains we are trying to point to our nameservers

I am not sure what to do further on my side, Thank you for any help in advance

Edited to add more details

I am trying to set up ns1 and ns2 as nameservers that other domains can use. I cant point any domains as they say ns2 is not returning with an answer on their servers below is a dig from 8.8.8.8 as I was asked to do in the comments

dig @8.8.8.8 ns2.iclixhosting.co.za

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-26.P2.el7_9.3 <<>> @8.8.8.8 ns2.iclixhosting.co.za
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 60456
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;ns2.iclixhosting.co.za.                IN      A

;; ANSWER SECTION:
ns2.iclixhosting.co.za. 3599    IN      A       164.160.80.20

;; Query time: 178 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Wed Feb 17 21:11:17 SAST 2021
;; MSG SIZE  rcvd: 67

As I say I am returning an answer however I cant set ns2 as the nameserver for other domains

Edited to add more details

Alright so thanks to Håkan Lindqvist in the comments I ran the command below and got the following results, This is very strange because if I ping the ns2.iclixhosting.co.za I get a response from the server

dig @ns2.iclixhosting.co.za heavencloud.co.za +norec

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-26.P2.el7_9.3 <<>> @ns2.iclixhosting.co.za heavencloud.co.za +norec
; (1 server found)
;; global options: +cmd
;; connection timed out; no servers could be reached

Another Edit

dig results

Answer 1

It look like the TCP port 53 is firewalled on NS2

nmap -p 53 ns1.iclixhosting.co.za 
Starting Nmap 7.91 ( https://nmap.org ) at 2021-02-18 10:50 CET
Nmap scan report for ns1.iclixhosting.co.za (164.160.80.18)
Host is up (0.20s latency).

PORT   STATE SERVICE
53/tcp open  domain

Nmap done: 1 IP address (1 host up) scanned in 0.82 seconds

VS

nmap -p 53 ns2.iclixhosting.co.za  -Pn
Host discovery disabled (-Pn). All addresses will be marked 'up' and scan times will be slower.
Starting Nmap 7.91 ( https://nmap.org ) at 2021-02-18 10:51 CET
Nmap scan report for ns2.iclixhosting.co.za (164.160.80.20)
Host is up.

PORT   STATE    SERVICE
53/tcp filtered domain

Nmap done: 1 IP address (1 host up) scanned in 2.11 seconds

could you please list open port on ns2 ? ( ss -ntpl for tcp open port on debian )