HMRC

Yesterday completely out of the blue I received a letter from HMRC saying my late H had overpaid income tax by £48.89 in the tax year 2017/2018 and enclosing a cheque made payable to me.
Today I received two more letters ,one saying he had overpaid the sum of £14and a few coppers for the same year and saying a cheque will follow.
The other letter said that in the tax year 2016/2017 he underpaid by £154 and asking me to pay it by Nov4th.
Two points arise, how do they ever function and can they ask me to pay this?