Mr Chilemba is a small-scale farmer in the Mkushi District of the Republic of Zambia. In order to expand his farming activities, he approaches Calendar Bank (the Bank) for a loan of K75,000 on 23 April, 2019 repayable on 31 October, 2019.

In view of the fact that the Bank was unwilling to advance the loan to Mr Chilemba, his former classmate at University: Isacc Mabunda, makes an undertaking to the Bank that, should Mr Chilemba fail to pay back the loan on the due date, he will settle the amount. The Bank thereafter proceeds to advance said loan to Mr Chilemba.

On 31 August, owing to Mr Chilemba's extravagant expenditure at the post 93rd Agricultural and Commercial Show festivities, he was only able to save K15, 000 towards settling the loan. Isaac does not want to have anything to do with the transaction, and requests that he be left in peace. The Bank approaches your consultancy on how it should proceed.

Please explain to them the relevant legal principles and advise accordingly