"Blacklisting" a phone without reason

I have been having a problem with my phone being "blacklisted". The phone has been in service and functioning for 4.5 years and recently in July 2018 my phone started giving me a 'sim network unlock pin' prompt that at first I mistook for a puk number; however, I have never had a sim pin on my phone.

Now realising that I am coding the wrong pin I eventually called Cell C regarding my problem and NO ONE, neither the consultants nor the TECHNICAL SUPPORT TEAM from Cell C seemed to recognise this sim unlock pin. Even today when I had called, no one has an idea of my problem.

Now, because the phone was originally bought at MTN I called their service centres and visited their stores to enquire about my problem. The manager at the Mall if Africa store, after having spoken to the front desk consultants, told me my phone was blacklisted. I was advised to write an affidavit and bring the phones proof of payment, I would have done that but problem was the phone was never ****** nor was it a contract phone so I had no statement to write regarding my phone's condition. I called the service centre to ask if my phone had been blacklisted, and apparently not. MTN also realised that I had not used their network for over 3 years and they informed me that there was nothing they could do because I was not active in their system anymore. One supervisor (from MTN) and a consultant from the BlackBerry department (from Cell C) informed me of the processes required for any individual to block my phone, which would be provide ID number and the IMEI number of the phone - no one had access to these details. Going back to Cell C and explaing this incident, yet again, and explaining to them that this prompt had occurred when I was using their network I was told by every consultant, technical support consultant and supervisor that I could not be assist because the problem is not with my sim card and those are the only queries that could assist me with. One supervisor had even told me to code the puk number - exposing the geeat length of information the network provides it's servuce consultants.

Prior to this, I first started at a Samsung store and the technical support member there had explained to me that they would not block a phone but rather it would be the service providers; the only assistance they could provide me with would be to change my entire phone board which would cost me R2000+, especially because my phone is a 2013 model.

Now my phone has been off service from the week of the 6th of July 2018 until today 07th October 2018. Internet sites sell packages from overseas at over R500 but I should be our service provides that also have these pins because they also buy phones for their networks and upon requesting a phone to be blacklisted, it would be an obvious scenario that they do keep these pins. This is in reference to Cell C telling me "they do not keep pins".

Now I am not sure who should help me in my case. Cell C, MTN or Samsung? Again, how was my phone locked when I had been using the same sim card (Cell C) for more than 4 years on PRE-PAID and yet I get this problem, and it is no one's fault? My phone appears to be not blacklisted on any service network but my phone will not support any sim card?

PS. I will add the names of every individual I have spoken to regarding my problem until I have my phone fixed and someone taking responsibility.