Sorry to hear about your plight @meno . Money lenders and asset vendors often employ stratagem with the underlying purpose of entrapping people in debt. Especially younger people who do not at the time fully understand the potential ramifications or fiscally insecure people who feel they have no other options. In many cases i find this practice despicable. However ultimately responsibility lies with the victim/offender (more than one way to look at it if i try to remain impartial)
I will attempt to offer some friendly advice - its only advice this doesn't mean its good advice, you will be the judge of that but I offer it freely and in good faith.
Your anxiety is something perhaps based on the reality of the situation. The flight mode life hack you mentioned although ingenious appears to me to be an anxiety containing measure, which may help short term but long term the debt is still there and the old enemy anxiety will adapt and evolve and could return and plague you. Anxiety has a horrible ability to do this.
Maybe it is time to steel yourself, grit your teeth and hold your head high.
Seek aid and assistance through official channels to consolidate your debt. Consolidated debts can often be vastly reduced payments on what would be needed to repay each individual debt. Not sure where your from but i found this with google search:
similar services are available in the UK where i come from
https://www.gov.uk/options-for-paying-off-your-debts
Should you achieve this then the collectors have no right to call on you. If they do you can answer your phone in confidence and if needed use a passive aggressive tone to inquire why they deem it necessary to harass you when you have taken the responsible steps within your power to resolve the debt. They often lose the smell of blood at this point and realise they can either accept smaller payments over a longer period of time or risk the debt being absolved.
Perhaps consolidation is not the answer for you but there are other options as mentioned in previous reply's to your post such as bankruptcy.
Whatever you decide to do I urge you to not only use containment measures, but also use a long term stratagem to eliminate the scourge of anxiety from your life just as long term strategy is used to dishonourably entrap many vulnerable people in an endless cycle of debt it also has the potential to free them.
Best of luck to you @meno there is light at the end of the tunnel and a man of your intellect has every chance of reaching it.