This is clearly the case of negative reference. Negative references can undermine your hard work overnight. Some employers are not willing to leave the past in the past and send references that hurt your chances and can cost you career advancements. For cases like this, a more proactive approach to a professional reference list is needed. Keep the following points in mind to avoid negative influence from ruining your career:
1. Clarify the situation
While it may seem obvious to avoid including an employer on your professional reference list you believe will give a negative report, many neglect this pertinent step and insist on referring hiring managers to companies that hold them in less than perfect esteem. You also can ask a colleague to call and see what the reference would be before including it on your professional reference list. If the review is negative or unconfirmed, do not list the company as a reference. If you do not think your past employer will give you a positive review, it's better to cut your losses and leave them off your reference list altogether.

2. Have a conversation
If a negative reference is unpreventable and your former boss has already hurt your reputation, it is time to reach out and negotiate a truce. Call your former boss and ask if they would be willing to agree to a future reference call. If the conversation doesn't look like it is going to accomplish anything positive, be assertive and explain why you think it is unprofessional and counterproductive to both sides. Many employers will feel pity for your mistake, especially if you were young and just starting out, or they may fear legal recourse.

3. Establish the true story
Sometimes the bad item on your professional reference list is a case of a misunderstanding or some form of inaccurate information. If the reference is factually inaccurate, skip your former boss and go straight to the Human Resources department. This may seem extreme, but giving a bad reference based on false information is unethical and unprofessional.

4. Explain the situation
When you cannot avoid a bad reference or negotiate it away, explain it to potential employers. Warn them that the reference will not be a good one and take time to explain why. One of the most common strategies employed against a negative professional reference list is having more positive references.

5. Ask them to stop
For negative references that do not cross legal boundaries, tell them to stop giving damaging references. This is particularly effective if the information is not accurate and could hurt your reputation unwillingly. List the name, complaint, and negative reference material in the letter. Tell them what they are doing, why it hurts your job prospects, and to stop sending negative references.

6. Get others involved
But if you cannot convince your previous employer to stop, legal action may be required. Many companies prefer to prevent court actions and will simply stop sending references of any kind.
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath