"Extremely poor service"

Referred by GP, as I had a blood clot in my artery, no cause to what the cause, since July 2024 I have been on blood thinners until a cause is found. I got an appointment to attend in person 13 weeks after the GP referral, 1 day before appointment the consultant calls to say a telephone conversation will be sufficient, refers me for bubble echo for potential hole in heart, said I may need other tests too if that is negative. I waited 8 weeks for the test. Waited for the results for 6 weeks. Another 6 weeks and counting since the publishing of those result I have had no contact from the consultant or his department, in the interim I called the hospital on the general number they try to connect with cardiology department with the consultant, who I will not name, never anyone there. I was given the number to try myself and always it goes to voicemail after ringing, I have left numerous messages and no one has ever got back. I need these test complete as being on blood thinners has impacted my work as there are duties I can not carry out as they may lead to injury. I am getting anxious and being on thinners for nearly a year may have more potential hazards in the near and far future. I understand the NHS is under pressure but this is ridiculous. How much longer do I wait and suffer?