I lived in the UK for 2 years back in 2019, but left when my student Visa ended. When I left I still owed a mobile contract, and had a credit card with a small balance on it.
I am now going back to the UK to visit friends, and will only be there a few weeks.
Will I be stopped at the airport or arrested?
Have you had any contact with the mobile phone company or bank since you left the UK?
Can you afford to pay the accounts?
For leaving unpaid bills or accounts behind in the UK alone, you will not be stopped or arrested.
You may wish to check the requirements to enter the UK from the country you are now living in, and insure you meet those requirements, this due to the Covid restrictions on travel here in the UK, and travelling to the UK.