They will usually give you an appointment regardless of the result. I have always received at least a phone appointment and usually an in-person appointment for any results. In fact, I have an in-person appointment next week to get the results of a biopsy the consultant even considered cancelling because he thought it unnecessary and he gave me the appointment before I had the biopsy, so it couldn't be because he found anything.

I doubt they would just send you a letter saying you were all clear. Apart from anything else, you might have questions for them, such as what else might be causing the ulcers and if you needed any further treatment to get rid of them.

I don't think that anything that happened is indicative either way. Scans cannot diagnose thyroid cancer anyway. At most, they can say if there is a nodule there, so even if they have found a thyroid nodule, the odds are that it is benign. About 95% of thyroid nodules are benign, so if they found a thyroid nodule, they would have to arrange a biopsy, which would be very likely to tell you everything was OK.