mak minah... Rank so fast up ah..
Since kena splashed paint already then report to your IO and go to the station and make another report together with the letter. Hopefully there is some lead to catch your runner. Since your mum already change her number right, they wont be able to harass her but whoever you mum put as NOK will be next to get harassment. So inform them too so they wont be shock receiving calls from this idiots. Either ignore all unknown numbers or if pick up tell them to deny knowing your mum. To play safe just inform your neighbours as well, just in case they might harass your neighbours. Dont need to tell them your mum borrowed just tell them she was scammed. Maybe lost her IC or something. Ask them for help to look out for suspicious characters also, neighbours are the next best thing to help you out when you are not around.
Good luck! Hopefully all will end soon, take care!