I had a similar issue with Seat24.de (same as G2G) on the OSL-DOH-BKK reservation. Illegal connection due to schedule change. Originally I had the 787/380 combo and they offered to move me on the later flight which is 777. I declined and requested to be rebooked a day earlier. Agent had no problem with that, I was rebooked in D instead of I.

After seeing the new booking on QR, agent informed me that it will take 24-48 hrs to receive my etickets as travel is not until September. Well, a few days passed and nothing, of course QR cancelled the flights as etix were not reissued.

I applied the same procedure again next week. Same thing, this time agent assured me that they are talking to QR ticketing to have it done in an hour max. Agent rebooked me in Economy (W) instead of business. Second call, things got sorted out quickly, and agent told me I am getting the new etickets in an hour. Well, two days later - nothing, rebooked flights got cancelled.

Today I called again, explained the issue and told the agent I will hold on the line until I get the new tickets and I am done dealing with this. It took good 20-30 mins, but I got rebooked and reticketed.

Just for your information.

Tickets were purchased through an OTA, even though QR made the schedule change and illegal connection, it is ALWAYS up to the OTA to fix things and talk with QR.

OP has to deal only with the OTA, QR cannot and will not help.