In your case, with you going much smaller there, was probably some suturing both on the sides and in the bottom of the old breast pocket to make it smaller to accommodate the newer smaller implant. This strapping type mechanism which can be done many different ways is meant to take the tension off of the repair so that you have time to heal without putting a stretch to a fresh suture line. Certainly,if you are having pain you can loosen the dressing some to asses it and then replace it. Get in touch with your plastic surgeon and find out what his or her thoughts are.
Post op breast augmentation garment
Many different surgeons have techniques to help give you the best results after breast augmentation. It is common to have a compressive wrap or bra placed immediately after surgery. The supportive tool used should provide support while the breasts heal and the capsule is forming as well as decrease the pain from your tissues holding up the implant. Whatever garment is used should be snug but not too tight as this can be extremely painful, cause more swelling and could affect wound healing.
It may be helpful to try and loosen the strap you are wearing or try wearing the bra without the wrap. I'm sorry you have not had contact with your surgeon, but continue to try so that you can discuss the situation with them.
Ultimately, don't keep yourself in unrelenting pain, if you need to remove the strapping even temporarily, you should do so, if unable to connect with your surgeon.