Kipling Bag missing!?

On 2 July 2017 I gave them my Kipling bag for a zip repair. I was told it will be about 3 weeks and they will SMS me when it's ready for collection. I called after about 5 weeks and was told the bag did arrive but they notice the zip was still broken and sent it back.

From there on it was phone call and going to the store in Clearwater Mall. I was eventually told, after about 3 months that the if the bag is over 4 years old (I bought it in 2012 but don't remember what month), then the zip would have to be replaced as Kipling changes the styles and the zip no longer in stock..or something! They quoted me R300/R450 for a black zip to be put into a blue/grey bag!

After another session of calls and visiting the shop I got to speak to someone at the Fraser factory and she promised to get it sorted. I then received a call to say they can replace the zip now for R150 and is it acceptable....that's after I said that it's ridiculous the price they quoted before and I won't pay as it's been so long!!!

So a month later I still don't have the bag! I sent a message to them on Facebook the other day to say that I refuse now to pay the R150 as they MUST have lost the bag, BECAUSE where is it??

Can I sue them for '*****ing' my bag?