UK passport needing more than 5day stay in shenzen

I am a Uk passport holder, i need to come to shenzen for 12 days, but don’t have enough time to get a chinese visa sorted.

can i fly to hong kong and use the 5 days VOA visa to enter shenzen, then just come back to hong kong after the 5 days and renew it and go back. So that i can get my 12 days in shenzen?

or is there an easier way?

Also if i overstay the 5 day visa im shenzen, and then come back to hong kong after 12 days what will happen?

thanks in advance