Has the sim card been replaced, or has the original been reused?
Four units sounds like there's another problem to me, not that I know as much as you, about the system.
I was a maintenance technician (electrician) for 25 years, and no way would we replace something 4 times, twice maybe.
Seeing one working in another car, and fitting that one would eliminate the unit, or not.
I know what you mean, but what are the other options or possibilities? Furthermore Tomtom have agreed with me that the problem lies within their apparatus. Apart from today, the other units have at least worked or a week or two.
I have had over 40 years of being a maintenance technician myself, and then the business owner in the whitegoods industry (cookers, home laundry & dishwashers) I Recently sold the business with over 80,000 customers on my data-base. I accept perhaps a long way from the motor trade, but when it comes to component failure over product failure, there are similarities.
High on the nature of my business was the application of modules in the way of printed circuit boards as fitted to most of the products my company dealt with. These were rather unstable at times, and quite common to have a high failure rate. Therefore quite volatile. So despite four units having failed, I can't say I'm that surprised, especially when I look at this forum as well as the TomTom forum.
So knowing the likely failure rate, I'm not at all surprised to see a "bad run" on something.
Sim card on the Tom Tom comes as part of a new sealed unit. There is in fact a directive from Mazda that in cases of TomTom unit failure, the old unit must be returned to Mazda direct, and untampered to prevent the possibility of rejection of the service claim. Mazda will not allow the job ticket to be cleared for payment until this criteria has been satisfied. Exactly the same as the industry I have been in.
I have had similar issues in the trackers as fitted to my vehicles, all of them used Sim cards.
So in essence, this is a TomTom issue, it has been well documented, and in fact is a recognised problem. As long as it goes on I will pursue TomTom for a satisfactory conclusion, and in the interim updates to mapping and an extension to my live traffic facility.
I love the car, and I will not allow this episode with regard to a second rate ancillary product to degenerate the quality of the car as a whole. Sadly though in the eyes of some users could reflect badly on Mazda as they have endorsed a second rate product in what should be a first rate car.
At present I blame TomTom, but there again perhaps Mazda made a mistake in the choice of service provider.
Alex