Block Sender disappears from list

Hi, I keep tring to block a sender to my hotmail account. Their personal email address remains on the block sender list but their work email address remains on the block sender list for a few minutes only then disappears. I have tried deleting from my block sender list just in case there is not enough room. I am 'fed up' receiving these emails and need help please!

Check your safe senders list. Are they also listed there and need to be removed?

they are not in the safe sender list. Thanks