From original company:
Dear Custy,
I am writing to inform you that I am (moving; leaving; flying to the moon; going to a buddhist retreat etc) and my business will be taken over by XYZ services.
Please be assured that I have vetted them thoroughly and that they have an excellent reputation for customer care and diligence having been window cleaning since (WW2.) The owner/contact name is (name) and he will be in touch very soon.
If you have any concerns then please phone me and/or him and we will assist in any way we can.
Yours etc
Floggit and Skarper
The new business's letter:
Dear Mrs Custy,
By now you should have received a letter from Floggit and Skarper outlining the change to your window cleaning services. Please rest assured that we will make the changeover as smooth and easy as possible and that we can be contacted on (0123456) if you wish to discuss this.
As of (31st Julember) invoices/payment slips with relevant details will be posted with each "clean" for you to act accordingly. If paying by cheque send it to (us), or by bank transfer (give details).
We look forward to providing you with an excellent service.
Y/s
B. Brush
Newbroom and Sweep