I deleted Viber from my phone yet my contacts still received missed calls from me. How is this possible?
That is actually impossible, unless someone used your number and activated the account while having access to your phone, but even so it's a Sci-Fi thing if you wouldn't notice. Double check again and inform your contact that you don't have Viber installed anymore.
Secondly, report this issue to the developers: https://support.viber.com/customer/portal/emails/new