No Response from Travelstart

I have been using Travelstart for many years now with great success. All of a sudden, no response!!!

In 2020, Covid curbed all travelling and Travelstart informed me accordingly. However, in August 2021 I received notification from Travelstart that I can rebook my flight, using my booking reference. Since September 2021 I followed the procedure to change my bookings but I got ABSELUTLY NO FEEDBACK. I repeat the process every two weeks but still no response. It is the end of December 2021 and I still have not received any response from Travelstart. I am sure they are still in business because the website is still active.

I have tried to call them (no telephone number on their webpage anymore) but also without success. I am out of options and ideas!