Unfortunately unnecessary stress caused

Following change of tyres a warning light came on early on a long journey. Consulting the handbook it said to stop and get it checked - but I was by this time on a motorway with at least 4hrs drive ahead of me. Stopped at services and phoned ATS but they weren't able to explain the warning light or what to do about it other than to go to another ATS. This was not an option at that time, nor the following day when I was in meeting all day. The result was I had to drive 500 miles driving slowly and worrying about a warning light telling me there was a fault with the tyres. I resolved it once back when someone kindly explained to me that cars with tyre monitors have to be reset after changing the wheels. I've always been elsewhere for tyres and never had this problem before so they obviously know to do this. Its such a simple matter of pressing a button hidden in the glovebox. No idea why ATS couldn't have done this.
They also put Nitrogen in the tyres without explaining to me that apparently I cannot now put air into them. I don't know if this is true but had I known I wouldn't have been persuaded.
Staff were friendly at the centre and the work was done promptly but the unnecessary stress caused means I shall return to avoiding ATS in the future.