I guess it may be the problem of single chip microcomputer, the internal clock is broken, or the power-on reset circuit of CPU is broken, which leads to the confusion of the program and the relay keeps switching. Or there is something wrong with the control circuit of the relay switch circuit, so it can only be thrown away.
It is also possible that there is an error in your own setup program and you have to readjust it yourself.
Dozens of dollars is not worth repairing, so how much does it cost to change a CPU? If the warranty is different.
If it is really repaired, call the manufacturer for repair.