If when it stops working you still have full voice recognition access, then it ought to be a Tesla end fault rather than an in-car fault. 2016 puts you in the era of permanent free connectivity (I think) assuming you are the first owner - otherwise it’s not unheard of for Tesla to argue that it doesn't transfer - much as they did with free charging. If your entitlement is for permanent connectivity then call Tesla and they have an obligation to put it right unless it's an in-car fault that requires your expense to fix. A full power-off reset may be worth trying first.