I can't see any reason to make contact with anyone as compensation has been received and a refund of the overpayment and you have been put on the correct rate.
What else is there?
If you do not pay your mortgage for several months (or any other loan), the financial institution will ask you to repay the amount due on the balance in full. They do not ask for extra (except any additional interest on the non payment and any legal fees incurred in chasing the debt).
If your house is worth €500,000 and your mortgage balance is €300,000, the bank looks for €300,000.
If you REFUSE to repay, then as its a secured loan, they can then call in that security, (in this case the house) sell it, and from the proceeds deduct the balance that was due on the mortgage + any legal and selling fees and then they pay you the balance. They do not keep the balance for themselves.
In above example, if the bank got €500,000, they would deduct €300,000 + selling fees of probably €10,000 and then transfer back to you €190,000.
In the deep recession, houses were selling for far below what was owed, hence rare that there was an excess and in many / most cases banks actually wrote off any residue balance owing.
This is how secured lending works and its quite clearly explained the in terms and conditions you signed with your solicitor.