Is there a platform for reporting fraudulent telephone (or SMS) numbers in China?

Of course there is. You can call the police as soon as you encounter such a situation.

Tencent Guardian platform has also been reported. At present, this platform has jointly launched a one-month public welfare publicity campaign with the Ministry of Public Security. This activity means that if we want to put an end to fraudulent phone calls, we need the support and participation of netizens.

The software participating in this activity, such as Tencent Mobile Manager, has a one-click reporting function.