This is one where it may be more effective to make a claim to one's travel insurance for the theft rather than delayed or lost luggage. Because that is what happened. If the bag has not been returned by the thief to BA, the thief may well simply have tossed it rather than be bothered or concerned about having to deal with the authorities. They may also be somewhere inconvenient to the airport and not in direct contact with BA.
Indeed WorldTracer will not be updated until the thief returns the bag to BA and, at that point, it is easy enough for BA to find a routing from wherever in India back to you in Milan. That may be circuitous and on other carriers, but this part is fairly routine.
BA may well disclaim any responsibility here as it apparently did deliver the bag as agreed. At a minimum, be prepared for a fight and bear in mind that this is about reimbursement, not compensation.
For the benefit of others, on those occasions when the generous cabin allowances are insufficient, I would be certain to pack valuables and items which are hard to replace or have sentimental value, in the cabin bags and then pack the replaceable items in the checked bag. From isolation replacement may be difficult, but hopefully there is someone or some service which can produce the necessities.