Please help! Saw a German cockroach in my house after professional treatment

I live in an apartment in a city (Barcelona). About two weeks ago I saw an American cockroach in my kitchen at night, and then two nights later saw another one. I immediately called pest control as I did not want for things to get out of hand. The pest control guy came and checked all the potential entry points and found nothing. No roaches, no eggs, no nymphs. He said it was possible that they live in the walls of the building and that it’s quite common in cities. He applied gel everywhere he thought was necessary and also applied this powder all around the possible entry points. He left some sticky traps with bait all the around the apartment.

Two weeks went by, we have not had a single sighting, not even a single one on the sticky traps. And then last night, just as I finally started to feel comfortable in my home again I saw a roach running out of a rug (the rug went straight to the bin) But this time a small one. I immediately messaged the exterminator and he confirmed it’s a German. He tells me that this has not come out of my house and was likely carried in from the outside or came from the neighbors. He says he can come and spray the kitchen if it will make me feel better but it would cost me a lot and would essentially be pointless since the source is not there.

I don’t know what to do. I’m in the process of turning the whole house upside down searching for them and deep cleaning. So far nothing found. I also got some poison traps as well that I will put all around. What else can I do? I feel so angry, and terrified, but also defeated since I seemingly did everything right and this still happened. Please help!