Usually customers contact support via their sales managers and customers of customers contact support via their re-sellers. However, if you bought the device via Amazon, it makes things a but more complicated.
First, I would try to contact the salesperson from Amazon. He would have direct contact with Teltonika (unless he himself bought the router from a re-seller). But since this is Amazon, I'm not sure what their obligations are. For example, it is unclear if they are obligated to provide technical support or not and probably depends on the seller.
In your case, you can go to Teltonika's website, click the "Contact us" button located on the right side of the screen, select the "Problem" category, provide a description of your issue and make sure to specify where you bought the router. You will be put in contact with a sales manager eventually.
However, Teltonika may take a long time to respond to such queries since you bought the router online and are not guaranteed any direct support from Teltonika. Furthermore, it is the holiday season and the staff returns to work January 2, 2019. So the period between now and this date will be slow for support.
