There is a point where a task stops being a task and becomes evidence. The unopened letters. The email from four months ago. The thing you said you would sort out and then avoided so long that dealing with it now means admitting how long it has been.
At that point you are not avoiding the work. You are avoiding the conversation about why it did not happen sooner, which is a completely different problem and considerably heavier.
The delay is almost always less interesting to them than to you
Whoever you have to contact deals with delayed matters constantly. Call centres, landlords, councils, accountants and clinics all have processes for exactly this, because most of what reaches them is late.
The version of the conversation you have rehearsed, where somebody is shocked or annoyed, is very rarely the one that happens. Usually they ask for a reference number and move on.
What to say about the gap
One sentence, no story. Pick whichever sits closest to how you actually feel about it and use that.
Pick the one you are facing
“I know this has been outstanding for a while, and I would like to get it sorted now.”
“This is later than it should be. What do you need from me.”
“I have not dealt with this until now. Can you tell me where it stands.”
Do not explain unless they ask
The instinct is to justify: an illness, a bereavement, a hard year. If a reason is relevant to what they can offer you, give it. Otherwise it usually makes the exchange longer and more uncomfortable, mostly for you.
Acknowledge and move to the practical question. Almost every organisation is set up to answer the practical question and has nothing to do with the other one.
Open the letters before deciding it is bad
A pile of unopened post grows in the imagination at a rate the contents rarely justify. Often several are duplicates, a couple are marketing, and the actual problem is one item smaller than feared.
Opening them without doing anything is a legitimate first step. You are converting an unknown into a known, and the unknown is what has been costing you.
Late is a state, not a verdict
Almost nothing on a typical list gets worse for having been avoided, in the way the dread implies. Debts accrue interest and deadlines pass, and both are real, but the imagined catastrophe is nearly always larger than the actual position.
The way in is usually a phone call, and the preparation for that is in making a phone call you have been avoiding.