I am not a qualified priest but, I know this would help you.
You can reverse or, in other words, stop deeksha by two ways as mentioned in the Meru Tantra.
1.By telling the mantra to a cow.
By writing the the mantra on a bhurja-patra or a manu script and leaving it in a river which flows all over the year.
But be sure to leave the mantra deeksha, which cant ...