Electricity bill not paid by previous owner

I(28M) recently bought a house. This house was rented to a family by the owner. While buying the house he told us that he will pay the pending electricity bill whenever the new bill will be generated.

We received the bill in august and it was around 15k and wasn't paid by the owner or the tenants since March. The previous owner lives abroad and we have tried to call him and texted him over whatsapp but he hasn't responded.

The electricity connection is still registered with previous owner's name. I want to transfer it to my name but I guess we will have to pay the pending bill first. Now, I really dont want pay this pending bill which should be paid by the previous owner.

What should be the legal course of action in this case for me? Should I consult a lawyer for this? Will sending a notice or hiring a lawyer cost me the same as the pending electricity bill or maybe even more?
Any advice is appreciated - thanks in advance!