Cannot reset - don't have previous owner details

I bought the iPad second-hand. When I purchased it the store told me that I just need to reset via iTunes, however, I does not work. It is locked by the previous owner’s iCloud account. When I went back to the store they were unwilling to assist me and wanted to charge me to change the motherboard to a new one so that I can use the device. This quote was more than I paid for the iPad! Please assist - how can I use the reset it? I have an iCloud account but will not do it as it is not the same account that the iPad is locked with…