Paid an annual Pro subscription but only received 6 months. No charging monthly!

I paid $99.99 on June 2, 2019 for annual (12 month) Avast Pro subscription. Was charged today $11.99 for monthly. Completely unsolicited charge.

Hi, your Avast Mobile Security Premium (former Pro) annual subscription was renewed on 6th December for $11.99.
We do not have any record for $99.99 with your e-mail address. However, the price rather points to a PC product. Please contact our Support directly from the app’s Menu and send us some payment record, or specify what e-mail address you used for the purchase and registration. Thanks.