end of contract, 2 oustanding invioces

Hi all, just after a bit of advice on what our next step should be.

We had a contract with a company that has now ended but has two outstanding invoices (each for £7000) which are now at 123 and 152 days overdue (30 day EOM payment terms).We have sent email statements and spoke to them and they have promised that payment would be made etc. with nothing forthcoming.Would our next course of action be a letter before legal action (via MCOL) and layout that addition late payment compensation and interest as well as the legal costs will be added to this claim (detailing what amount this would currently be (excluding legal costs)) unless immediate payment or response is received by return? (Effectively the final reminder letter under the letter and forms section of this site).Many thanks for any advice or assistance.