Your handwriting is awful / careless / illegible / scratchy. 你的字跡太潦草了。 Please make it more clearer and...
... in Chinese. Please let me know if you find it full of illegible codes. 亂碼: illegible codes/words/text/characters...
...date. (For example, you could say that because the stickers are illegible because of dust or water ingress), and then forward their response to us.