Hello and welcome to the forum,
When you get these thoughts, you can recite:
A'oodhu billaahi minash-shaytaanir-rajeem
(I seek refuge in Allah from Satan, the rejected)
You can listen to what it sounds like here - it's the very first phrase recited:
Ignore what these thoughts are telling you and In sha Allaah (God-willing) they will go away. May Allaah :swt: help you to take the shahadah as soon as possible, Aameen.