MTN Insurance use companies that put **** parts instead of Treating customers fairly

I have mtn insurance for my iPhone 8Plus, last year Feb I submitted a claim because my phone fell and the entire back glass was shattered... I went to iStore first to see if I can replace the back myself instead of submitting a claim, I was told at iStore that they do not repair these phones if the back is shattered because no one in South Africa has original parts... i then submitted a claim with mtn, to my surprise mtn told me that they will be fixing the phone. I stated my concerns about the original parts and how iStore do not fix they replace, I was assured that WeFix use original parts and if I experience any issues they will assist me... Since the phone was “repaired” I’ve always had issues and I’ve taken the phone back to WeFix several times with various issues related to the back cover not synchronizing (issues such as volume button not working, sound not working, phone vibrating non stop for no reason)...

I went to iStore 31.01.2019 regarding the above mentioned issues and they made me aware of the fact that the back cover is ****, they placed my phone next to the iPhone8 Plus in store and the differences between the two phones is evident... The service technician tells me that because the phone has been tampered with and does not have original parts they will not touch or make any repairs on the phone...

I called mtn with my problem and was told I need to call a company called monitor as this is not their problem, the company has changed and they are the ones that dealt with my original claim... I called the number I was given and that company told me that they no longer work with mtn, I need to call mtn they must assist me...

I called MTN back and was told I need to submit a new claim but they do not replace phones unless the phone is lost or ******... I said I’m not opposed to submitting a new claim but will it be possible for me to send the phone to iStore for assessment and get the report they need from there... I was told no they use they own assessor only, they same assessors that will say the phone can be repaired and more **** parts will be added to my phone... I don’t know what to do because I cannot even take my phone in for repair myself because of the **** parts on a phone which I purchased brand new from MTN with ORIGINAL parts...

My insurance company had failed me even though ever month my premiums get paid on time no hassle... I need a way forward