Has OTG ever worked in your tablet?
Though not entirely accurate (according to the comments) try this app and see if it is even available in your tablet
Did the optical mouse' light come on when you connected it via the OTG? You didn't say.
If it didn't it means that the tablet either didn't "know" that an OTG adapter was connected, or it did and that there was no power turned onto the tablet's USB port.
Sorry to bore you but the way it works is as follows:
Normally your tablet is considered as a USB device. That means that there is no +5VDC power being supplied on pin 1 of the tablet's USB port.
The USB connection works when you connect to a PC because the PC supplies the power on pin 1 as it is a USB host.
When you connect an OTG adapter to the tablet's USB port, because the OTG adapter has a wired connection between pins 4&5 in the USB connector that plugs into the tablet, the tablet "knows" (because there is now an earth potential on pin 4) to change into USB host mode and supply +5VDC onto pin 1 of the USB port, thereby supplying power to a connected USB device such as a mouse.
First use a magnifying glass and a strong light to visually inspect the tablet's USB port enclosure. Ensure that all 5 pins are there and that they are straight and parallel with each other. Also check that there is no dust or lint trapped in the port. If there is use a vacuum cleaner to suck it out or if necessary a wooden toothpick to gently prise it out.
If the port looks OK use a DMM (Digital Multimeter) voltmeter to check that there is +5VDC on pin 1 of the OTG other end USB plug when the OTG adapter is plugged into the tablet. (connect DMM between pins 1 & 4)
If there is no voltage you'll need to open the tablet to investigate further.