Regarding Payment from a company

Dear Sir Greetings! please give me the advice for release of our payment from a company. I am briefing the case as below; 1. We received Purchase Orders for laboratory incubators from a reputed pharma company. 2. we submitted the Bank guarantee of 20% amount of the Total Order Value to the company. It was promised by company that on receiving the material they will release 80% of the payment, 10% payment will be released after installation and rest 10% will be kept as performance security. 3. After a satisfactory visit of the company engineer and his positive report, We send incubators to the company and they received them. We confirmed them that on receiving the part payment as per PO we will send our engineer for installation. 4. The company denied the payment and forced us for completing the installation first. 5. After 5 days the company suddenly send us an e-mail stating that the PO is being canceled giving the false reasons of Quality issues. 6. We requested the company that if the quality of our incubators was not OK why their enginer send the positive report and further they received the incubators after through quality check. Then how all of sudden the quality has become an issue of non-payment. 7. I send several mails to them to get the installation completed and release of our Bank Guarantee and payment. But the company never replied. 8. Then on expiry of our Bank Guarantee (BG) the Bank send two tracers to the company asking if they have any objection on the release of BG but they did not reply to the Bank Tracers also and finally we got the BG released by the Bank. So, The company neither replied to our e-mails nor to the tracers of Bank. Please let me know how can we get our payment from the company. Also, please suggest this issue is now 10 months old does the terms and conditions of Purchase Order still valid however, after sending the e-mail of cancellation of the PO they company neither send us any legal notice nor replied to our email or Bank Tracers.