I cleared my ielts exam with overall 7 bands after that I also did some work on my speaking skills but still not able to crack university credibility interview. I am feeling demotivated right now . I don't know what I should do .

Have you tried other universities? Top-tier universities select only one out of twenty or even fifty applicants. Others are much less stringent and have a lower bar to entrance.

Students: We have free audio pronunciation exercises.
Yes, i have applied in other universities like Lincoln and bpp but their addmission process is bit slow.

So you just need to be patient. Apply for many universities.