OP, I wanted to add a few more thoughts as this has been on my mind all night and kept me awake. (On my part, I am someone who has been dealing with breast lumps for 30+ years, the first of which was when I was 15. I was eventually diagnosed with breast cancer at 47. In the interim, have had dozens of trips to various breast clinics and consultants, numerous biopsies, and several lumpectomies.
With all this in mind, You are totally getting ahead of yourself and worrying about an outcome that might well not happen for you. There are any number of reasons to be called in for a face-to-face after finding a lump/attending a one stop clinic (or similar). Yes, cancer might be one of those things, but the initial biopsies might have been non-conclusive and indeterminate. In this instance, they will want to perform another biopsy or even schedule a surgery to investigate further. Both these things have happened to me. Or, perhaps there is something in your medical history, either your own or your family's, maybe your background/ethnicity that they want to discuss with you - it could be as simple as the fact they think it could be worth talking to your about genetic testing to see if you carry a gene mutation. Again, this is also something I have been asked to come in to discuss.
Either way, at this moment in time, you know nothing other than you have a lump in your breast. First things first, go see your GP for a referral. Additionally, it is also worth considering your own timescale. By this I mean how long have you had the lump? I ask this because if you're still menstruating/not yet reached menopause and it has been less than a month, it might well be hormonal and gone by this time next week. If you have had it for a few months, go now. Time really is of the essence, but, and I have to stress, the odds really are in your favour of it not being cancer. And if it is, you will be surprised by how well you cope. And if you do have it, breast cancer is rarely the killer it once was. I say this as someone in their family who is the first to get a cancer diagnosis and not die within six months. In fact, my maternal grandmother died from breast (and ovarian) cancer in her late 40s, my aunt died of breast cancer at 34. That was several decades ago and treatment for breast cancer has come on such a long way that the survival rates are excellent, more so if you have a hormonal cancer, and especially if it is caught early. For many, breast cancer is nothing more than a blip - a lumpectomy/breast conserving surgery, radiotherapy, and hormone treatment - no chemotherapy, no mastectomy, very little change to their lives, and something that never effects their lives again.
By avoiding not going and worrying about an outcome that might well not even effect you, is causing you stress, possibly for nothing. And if after everything it is cancer, there will be support for you, but most importantly, they will start gathering more information about you/your physiology - a huge part the initial cancer diagnosis face-to-face conversation is ensuring they take bloods that day and talk to you about other investigations they might need to do, be it more biopsies, an MRI and other scans. Being told you have cancer is just the beginning and very much the quiet before the storm of appointments. But, and like I said, all this is moot at the moment. Just concentrate on going to the GP.
Lastly, you asked what would happen if you refused to go in to discuss results (should you be asked to). They will keep calling you until you do. I say this as someone who managed to miss several voice mails asking me to come in. More often than not, the person who is calling you usually has zero idea of why you are being asked to come back in anyway, and even if they do, they are not allowed to discuss your results on the phone.
Take a deep breath, call your GP. Just get the ball rolling.