Textbooks.com Customer Service Issues

I am experiencing difficulty opening the Testbook app on my mobile device. When I try to open it, I am seeing the following error code on the screen: "java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference at com.google.firebase.installations.f.s(FirebaseInstallations.java:1) at com.google.firebase.installations.f.e(FirebaseInstallations.java:5) at com.google.firebase.installations.f.o(FirebaseInstallations.java:1) at com.google.firebase.installations.d.run(FirebaseInstallations.java) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:[redacted]) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:[redacted]) at java.lang.Thread.run(Thread.java:[redacted])".

Yesterday, I tried a sectional test on your website as a trial. Today, a caller claiming to be from your team offered me an 18-month package for Rs [redacted] not listed on the website, providing a link. I doubted his authenticity and blocked him, but he contacted me from another number and continued messaging me. He even tried a video call on Whatsapp, which I ignored. I am unsure if he is legitimate.

I ordered 3 books from the Testbook app. Two books on December 3rd: "Best [redacted] Q Bank SSC General Intelligence and Reasoning" and "Best [redacted] Q Bank SSC English Language," and one book on December 4th: "Best [redacted] Smart Q Bank SSC Quantitative Aptitude" in English. I have paid the full amount. I have reached out multiple times via email on Testbook but only received computer-generated responses with no updates on delivery or tracking information. Today, I attempted to contact Testbook's customer care number 10-12 times, but I only heard a busy signal. Please share the tracking number with me.