Is it known around when the books are set in? They have no computers or cell phones but they do dress a bit modern. Thanks

I believe there was a Q&A video where he said that it's basically modern day, but the technology is very far behind because people have been more focused on the Problem than on tech for personal use

Yeah, the setting is contemporary. I worked the following out around book two, from the mentions of dates and characters' ages:

• 1950s Scattered sightings in Kent and Sussex "around the middle of the last century".
• 1960s Major cases "a decade later"; Fittes and Rotwell active.
• late 1990s Lucy born in the "fourth official decade of the Problem".
• 2010s Lockwood and Co active

Stroud has confirmed that the Problem has significantly slowed down the world's technological development, as so much of the economy's research and manufacturing capacity is fed into dealing with the Problem, while the number of children taken out of school and packed off to work as night watch or agents also has significant knock-on effects on the education level of the workforce.
I place the tech level as stuck somewhere around the 70s or 80s, given the above timeline and the tech we've seen - which would mean that computers exist, but they're probably restricted to a handful of educational establishments and very large businesses. (Early development of computing predates the Problem, so some sort of computing definitely exists, it's just a question of how far development got before suffering significantly from lack of resourcing.)