You should always check if there is a known scam when you receive an unusual email. If you google Viber International Ballot Award Programme you will get many scam alert warnings. You were right to be wary OP but spelling/ grammar errors can sometimes be due to predictive text when you type one thing and it can be changed without you noticing or ever just poor education. I recently received an email genuinely from the tax office with glaring spelling and grammatical mistakes. I called in to check (not to the number on the email) and whilst I was reassured that the communication was genuine I was surprised that the person I spoke to seemed unconcerned that the communication had errors.
Thanks for helpful tips to catch scammers. I think sharing a personal experience with others important to make others aware. I always try to avoid these kinds of phone calls and most important don't share OTP in any case.